Match charting Archives - Page 5 of 10

Dayana Yastremska Hits Harder Than You

At the 2019 Australian Open, tennis balls have more to fear than ever before. Serena Williams is back and appears to be in top form, Maria Sharapova is playing well enough to oust defending champion Caroline Wozniacki, and Petra Kvitova has followed up her Sydney title with a stress-free jaunt through the first three rounds.

And then there are the youngsters. Hyper-aggressive 20-year-old Aryna Sabalenka crashed out in the third round against an even younger threat, Amanda Anisimova. But still in the draw, facing Serena on Saturday, is the hardest hitter of all, 18-year-old Ukrainian Dayana Yastremska. Watch a couple of Sabalenka matches, and you might wonder if we’ve reached the apex of aggression on the tennis court. Nope: Yastremska turns it up to 11.

When Lowell first introduced his aggression score metric a few years ago, Kvitova was the clear leader of the pack, the player who ended points–for good or ill–most frequently with the ball on her racket. Madison Keys wasn’t far behind, with Serena coming in third among the small group of players for which we had sufficient data. Since then, two things have changed: The Match Charting Project now has a lot more data on many more players, and a new generation of ball-bashers has threatened to make the rest of the tour look like weaklings in comparison.

The aggression score metric packs a lot of explanatory power in a simple calculation: It’s the number of point-ending shots (winners, unforced errors, or shots that induce a forced error from the opponent) divided by the number of shot opportunities. The resulting statistic ranges from about 10% at the lower extreme–Sara Errani’s career average is 11.6%–to 30%* at the top end. Individual matches can be even higher or lower, but no player with at least five charted matches sits outside of that range.

* Readers with a keen memory or a penchant for following links will notice that in Lowell’s orignial post, Kvitova’s aggregate score was 33% and Keys was also a tick above 30%. I’m not sure whether those were flukes that have since come back down with larger samples, or whether I’m using a slightly different formula. Either way, the ordering of players has remained consistent, and that’s the important thing.

Here are the top ten most aggressive WTA tour regulars of the 2010s before Sabalenka and Yastremska came along:

Rank  Player                      Agg 
1     Petra Kvitova             27.1%  
2     Julia Goerges             26.8%  
3     Serena Williams           26.8%  
4     Jelena Ostapenko          26.5%  
5     Camila Giorgi             26.0%  
6     Madison Keys              25.9%  
7     Coco Vandeweghe           25.9%  
8     Sabine Lisicki            25.6%  
9     Anastasia Pavlyuchenkova  24.0%  
10    Maria Sharapova           23.2%

All of these women rank among the top 15% of most aggressive players. They end points more frequently on their own racket than plenty of competitors we also consider aggressive, like Venus Williams (21.9%), Karolina Pliskova (21.6%), and Johanna Konta (22.3%). Ostapenko bridges the gap between the two generations; she wasn’t part of the discussion when aggression score was first introduced, though once she started winning matches, it was immediately clear that she’d challenge Kvitova at the top of this list.

Here’s the current top ten:

Rank  Player               Agg  
1     Dayana Yastremska  28.6%  
2     Aryna Sabalenka    27.6%  
3     Petra Kvitova      27.1%  
4     Julia Goerges      26.8%  
5     Serena Williams    26.8%  
6     Jelena Ostapenko   26.5%  
7     Viktoria Kuzmova   26.0%  
8     Camila Giorgi      26.0%  
9     Madison Keys       25.9%  
10    Coco Vandeweghe    25.9%

Yastremska, Sabalenka, and even Viktoria Kuzmova have elbowed their way into the top ten. Yastremska’s and Kuzmova’s places on this list might be a little premature, since their scores are based on only seven and nine matches, respectively. But Sabalenka’s pugnaciousness is well-documented: her Petra-topping score of 27.6% is an average across almost 30 matches.

Tennis tends to swing between extremes, with one generation developing skills to counteract the abilities of the previous one. It’s not yet clear whether the aggression of these young women will catapult them to the top–after all, Sabalenka won only five games today against Anisimova, whose aggression score is a more modestly high 23.0%. Perhaps as they gain experience, they’ll develop more well-rounded games and return Kvitova to her place at the top.

In the meantime, we have the privilege of watching some of the hardest hitters in WTA history battle it out. Tomorrow, Yastremska will contest her first third round at a major in a must-watch match against Serena. There will be fireworks, but it’s safe to say there won’t be much in the way of rallies.

What I Should’ve Known About Playing Styles and Upsets

In the podcast Carl Bialik and I recorded yesterday, I mentioned a pet theory I’ve had for awhile, that upsets are more likely in matches between players with contrasting styles. The logic is fairly simple. If you have two counterpunchers going at it, the better counterpuncher will probably win. If two big servers face off, the better big server should have no problem. But if a big server plays a counterpuncher … then, all bets are off.

We’ve seen Rafael Nadal struggle against the likes of John Isner and Dustin Brown, and and we’ve seen big servers neutralized by their opposites, as in Marin Cilic’s 1-6 record against Gilles Simon. There are upsets when similar styles clash, as well, but as untested theories go, this one is appealing and not obviously flawed.

Then, to kick off the 2019 Australian Open, Reilly Opelka knocked out Isner. Playing styles don’t come much more evenly matched, and the veteran was the heavy favorite. It was a perfect example of the kind of match I would expect to follow the script, yet the underdog came out on top. They played four tiebreaks and there were only two breaks of serve, but Opelka didn’t even need the Australian Open’s new fifth-set 10-point tiebreak. While it’s just one match, of course, it suggested that I ought to look more closely at my assumptions.

After a couple of hours playing with data this afternoon, my theory is no longer untested … and it turned out to be flawed. Fortunately, it isn’t just another negative result. Playing style is related to upset likelihood, but not in the way I predicted.

Measuring predictability

Let me explain how I tested the idea, and we’ll work our way to the results. First, I used used Match Charting Project data to calculate aggression score for every ATP player with at least 10 charted matches since 2010. Aggression score is, essentially, the percentage of shots that end the point (by winner, unforced error, or inducing a forced error), as will serve as our proxy for playing style. That gives us a group of 106 players, from the conservative Simon and Yoshihito Nishioka with aggression scores around 13%, to the freewheeling Brown and Ivo Karlovic, with scores nearing 30%. I divided those 106 players into quartiles (by number of matches, not number of players, so each quartile contains between 21 and 31 players) so we could see how each general playing style fares against the others. Here are the groups:

Q1: The least aggressive players, with scores from 13% to 16%. Includes Simon, Rafael Nadal, Andy Murray, and David Ferrer.
Q2: Less aggressive than average, but not pure counterpunchers; scores from 16% to 18%. Includes Novak Djokovic (who is just above the border with Q1), Juan Martin del Potro, Kei Nishikori, and David Goffin.
Q3: More aggressive, but not one-dimensional, with scores from 18% to 20.7%. Alexander Zverev is just above the line with Q2, and the group also includes Dominic Thiem, Tomas Berdych, and Stan Wawrinka.
Q4: The biggest servers and otherwise high-risk players, with scores above 20.7%. Roger Federer just barely makes the cut, and he’s joined by players like Jo Wilfried Tsonga, Nick Kyrgios, and Milos Raonic.

(Aggression score conflates two things: big serving/big hitting and tactical aggression. Isner is sometimes not particularly aggressive, but because of his size and serve skill, he is able to end points so frequently that, statistically, he appears to be extremely aggressive. Accordingly, I’ll refer to “big servers” and “aggressive players” interchangeably, even though in reality, there are plenty of differences between the two groups.)

Limiting our view to these 106 men, I found just over 11,000 matches to evaluate and divided them into groups based on which quartiles the two players fell into. Each of the ten possible subsets of matches, like Q1 vs Q2, or Q4 vs Q4, contains at least 400 examples.

For every match, I used surface-adjusted Elo ratings to determine the likelihood that the favorite would win. That gives us pre-match odds that aren’t quite as accurate as what sportsbooks might offer, though they’re close.

Those pre-match odds are key to determining whether certain groups are more predictable than others. If there are 100 matches in which the favorite is given a 60% chance of winning, and the favorites win 70 of them, we’d say that the results were more predictable than expected. If the favorites win only 50, the results were less predictable.

Goodbye, pet theory

For the matches in each of the ten quartile-vs-quartile subsets, I calculated the average favorite’s chance of winning (“Fave Odds”), then compared that to the frequency with which the favorites went on to win (“Fave Win%”). The table below shows the results, along with the relationship between those two numbers (“Ratio”). A ratio of 1.0 means that matches within the subset are exactly as predictable as expected; higher ratios mean that the favorites were even better bets than the odds gave them credit for, and lower ratios indicate more upsets than expected.

Matchup	Matches	Fave Odds	Fave Win%	Ratio
Q1 vs Q1	412	71.1%	75.2%	1.06
Q1 vs Q2	1072	69.5%	70.6%	1.02
Q1 vs Q3	1382	69.7%	68.6%	0.98
Q1 vs Q4	1187	69.7%	70.0%	1.00
Q2 vs Q2	612	70.2%	69.9%	1.00
Q2 vs Q3	1616	68.8%	67.8%	0.99
Q2 vs Q4	1434	68.8%	67.4%	0.98
Q3 vs Q3	886	66.7%	60.3%	0.90
Q3 vs Q4	1685	67.3%	66.8%	0.99
Q4 vs Q4	791	67.1%	61.2%	0.91

There’s a striking finding here: The largest ratio, marking the most predictable bucket of matches, is for the most conservative pairs of players, while the smallest ratio, pointing to the most frequent upsets, is for the most aggressive players.

Before analyzing the relationship, let’s check one more thing. The very best players aren’t evenly divided throughout the quartiles, since Q1 has two of the big four. Elo-based match predictions–one of the building blocks of these results–are tougher to get right for the best players and the most uneven matchups, so we need to be careful whenever the elites might be influencing our findings. Therefore, let’s look at the same numbers, but this time for only those matches in which the favorite has a 50% to 70% chance of winning. This way, we exclude many of the best players’ matchups and all of their more lopsided contests:

Matchup	Matches	Fave Odds	Fave Win%	Ratio
Q1 vs Q1	196	59.5%	62.8%	1.05
Q1 vs Q2	604	59.8%	60.6%	1.01
Q1 vs Q3	731	59.7%	58.1%	0.97
Q1 vs Q4	663	59.9%	60.6%	1.01
Q2 vs Q2	322	59.0%	54.7%	0.93
Q2 vs Q3	931	59.8%	59.8%	1.00
Q2 vs Q4	822	59.7%	57.2%	0.96
Q3 vs Q3	544	59.5%	55.0%	0.92
Q3 vs Q4	1024	59.5%	58.2%	0.98
Q4 vs Q4	493	59.3%	55.0%	0.93

We discard about 40% of our sample, but the predictability trend remains the generally the same. In both the overall sample and the narrower 50%- to 70%-favorite subset, the strongest relationship I could find was between the predictability ratio and the quartile of the less aggressive player. In other words, a counterpuncher is likely to have more predictable results–regardless of whether he faces a big server, a fellow counterpuncher, or anyone in between–than a more aggressive player.

Back to basics

My initial theory is clearly wrong. I expected to find that Q1 vs Q1 matches were more predictable than average, and I was right. But by my logic, I also guessed that Q4 vs Q4 matches went according to script, and that other pairings, like Q1 vs Q4, would be more upset-prone. I would have done better had I let the neighbor’s cat make my predictions for me.

Instead, we find that that matches with more aggressive players are more likely to result in surprises. That doesn’t sound so groundbreaking, and it’s something I should’ve seen coming. Big servers tend to hold serve more often and break serve less frequently, meaning that their matches end with narrower margins, opening the door for luck to play a larger role, especially when sets and matches are determined by tiebreaks.

After all this, you might be thinking that I’ve squandered my afternoon, plus another few minutes of your attention, arriving at something obvious and unremarkable. I agree that it’s not that exciting to proclaim that big servers are more influenced by luck. But there’s still a useful–even surprising–discovery buried here.

Exponential upset potential

We know that the most one-dimensional players are more subject than others to the ups and downs of luck, thanks to the narrow margins of tiebreaks. For a man who rarely breaks serve, no match is a guaranteed win; for a man who rarely gets broken, no opponent is impossible to beat. However, I would have expected that the unpredictability of big servers was already incorporated into our match predictions, via the Elo ratings of the big servers. If a player has unusually random results, we’d expect his rating to drift toward tour average. That’s one reason that it’s very difficult for poor returners to reach the very top of the rankings.

But apparently, that isn’t quite right. The randomness-driven Elo ratings of our big servers do a nearly perfect job of predicting match outcomes against counterpunchers, and they’re only a little bit too confident against the more middle-of-the-road players in Q2 and Q3. Against each other, though, upsets run rampant. That extremely volatile fraction of results–the tiebreak-packed outcomes when the biggest servers face off–only accounts for part of these players’ ratings.

We’re accustomed to getting unpredictable results from the most aggressive players, with their big serves, inconsistent returns, and short rallies. Today’s findings give us a better idea of when these do and do not occur. Against counterpunchers, things aren’t so unpredictable after all. But when big servers play each other, we expect the unexpected–and the results are even more unpredictable than that.

Match Charting Project Update and New Template

The Match Charting Project is a crowd-sourced, volunteer effort to gather exhaustive shot-by-shot data on professional tennis matches. We’re closing in on the 5,000-match mark, and are building a wide range of meaningful datasets for subsets of players and matches. We have shot-by-shot records of nearly all grand slam finals, most Masters finals, many major semi-finals and Premier finals, all head-to-head matches between members of the Big Four, and nearly every match ever played by Simona Halep.

Here’s the complete list of charted matches, and here’s an example of the data assembled for a single player.

I hope you’re inspired by what we’ve already achieved to contribute to the project. We have several dedicated charters and over 100 people have charted matches over the lifetime of the project, but the more data we have, the more valuable the entire effort becomes. Click here to find out more about getting started.

The immediate impetus for today’s post is the updated Excel template I’m releasing today, version 0.3.0. Revising the template was a necessity ahead of the 2019 Australian Open, because of the unique new rules under which AO matches will be played. The template now handles several rules variations, including 2019 AO rules (a super-tiebreak at 6-6 in the deciding set), 2019 Wimbledon rules (a standard tiebreak at 12-12 in the deciding set), and ATP NextGen Finals rules (no-ad, first to four games, standard tiebreak at 3-3). We’ve already posted the first charted match from the NextGen Finals, last year’s title match between Tsitsipas and De Minaur.

If you’re already familiar with charting and the MCP Excel template, all you need to know is that you can enter “A” in cell B14 to indicate that the match is played under 2019 AO rules. (For 2019 Wimbledon, use “T”, and for NextGen Finals, use “N”.)

I’ve also made an addition to the shot-by-shot syntax to handle situations in which a player stops a rally to challenge (or have a mark checked) but is proven wrong. If you’re charting, check the Instructions tab in the new Excel template for more details.

Finally, the MatchStats tab now includes a running tally of total shots and average rally length.

For those of you who are already contributors to the MCP: Thank you very much for your efforts. For everyone else, I hope 2019 is the tennis season when you decide to give it a try.

Click here to download the new template.

The Right Amount of Serve-and-Volley

Embed from Getty Images

Italian translation at settesei.it

In modern tennis, players approach the net at their own peril, especially behind their serve. Technological advances in both strings and rackets have made passing shots faster and more accurate, giving an added edge to the returner. It’s hard to imagine the game changing so that serve-and-volleying would once again become a dominant tactic.

Yet pundits and commentators often suggest that players should approach the net more often, sometimes advocating for more frequent serve-and-volleying. In a recent article at FiveThirtyEight, Amy Lundy brought some numbers to the discussion, pointing out that at the US Open this year, women have won 76% of their serve-and-volley points and men have won 66%. She also provides year-by-year numbers from the women’s Wimbledon draw showing that for more than a decade, the serve-and-volley success rate has hovered around the mid-sixties.

Sounds good, right? Well… not so fast. Through the quarter-finals in New York, men had won roughly 72% of their first-serve points. Most serve-and-volley attempts come on first serves, so a 66% success rate when charging the net doesn’t make for much of a recommendation. The women’s number of 76% is more encouraging, as the overall first-serve win rate in the women’s draw is about 64%. But as we’ll see, WTA players are usually much less successful.

Net game theory

When evaluating a tactic, we have to start by recognizing that players and coaches generally know what they’re doing. Sure, they make mistakes, and they can fall into suboptimal patterns. But it would be a big surprise to find that they’ve left hundreds of points on the table by ignoring a well-known option. If more frequent serve-and-volleying was such a slam dunk, wouldn’t players be doing so?

I dug into Match Charting Project data to get a better idea of how often players are using the serve-and-volley, how successful it has been. and, just as important, how successful they’ve been when they aren’t using it. The results are considerably more mixed than the serve-and-volley cheerleaders would have it.

Let’s start with the women. In close to 2,000 charted matches from 2010 to the present, I found 429 player-matches with at least one serve-and-volley attempt. After excluding aces, regardless of whether the server was intending to approach, those 429 players combined for 1,191 serve-and-volley attempts–95% of them on first serves–of which they won 747. Had those players not serve-and-volleyed on those 1,191 points and won at the same rate as their first- and second-serve baseline points in the same matches, they would have won 725 points. In other words, serve-and-volleying resulted in a winning percentage of 62.7%, and staying back was good for 60.9%. Just to be clear, this is a direct comparison of success rates for the same players against the same opponents, controlling for the differences between first and second serves.

A difference of nearly two percentage points is nothing to sneeze at, but it’s a far cry from the more than ten percent gap we’ve seen on the women’s side at the US Open this year. And it might not be enough of a benefit for many players to overcome their own discomfort or lack of familiarity with the tactic.

When we apply the same analysis to the men, the results are downright baffling. We have more data to work with here: In nearly 1,500 charted matches from 2010 to the present, more than half of the possible player-matches (1,631) tried at least one serve-and-volley. About four in five–once again excluding aces–were first serves. The tour-wide success rate was similar to what we’ve seen at the Open this year, at 66.8%.

Controlling for first and second serves, the same servers, at the same tournaments, facing the same opponents, won points at a 72.2% rate when they weren’t serve-and-volleying. That’s a five percentage point gap* that says men, on average, and serve-and-volleying too much.

* Technical note: These overall rates simply tally all the serve-and-volley attempts and successes for all players. Thus, they may give too much weight to frequent netrushers. I ran the same calculation in two other ways: giving equal weight to each player-match, and weighting each player-match by ln(a+1), where a is the number of serve-and-volley attempts. In both cases the gap shrunk a bit, to four percentage points, which doesn’t change the conclusion.

I was shocked to see this result, and I’m not sure what to make of it. It’s roughly the same for men who serve-and-volley frequently as for those who don’t, so it isn’t just an artifact of, say, the odd points that an Ivo Karlovic or Dustin Brown plays from baseline, or the low-leverage status of the occasional point when a baseliner decides to serve-and-volley. Since I don’t have a good explanation for this, I’m going to settle for a much weaker claim that I can make with more confidence: The evidence doesn’t suggest that men, in general, should serve-and-volley more.

Data from the women’s game is more encouraging for those who would like to see more serve-and-volleying, but it is still rather modest. Certainly, the 76% success rate in Flushing this year is a misleading indicator of what WTA players can expect to reap from the tactic on a regular basis. It’s possible that some women should come in behind their serves more often. But the overall evidence from a couple thousand matches suggests sticking to the baseline is just as good of a bet–if not better.

New Match Charting Project Excel Template

For the first time in more than two years, I’m ready to release a new, substantially improved version of the MatchChart excel template, the platform on which volunteers log matches for the Match Charting Project.

New in version 0.2.0:

Color-coding of the players, as well as game-ending and set-ending rows, to make it easier to keep track of where you are in a match;
A new shot code for drop volleys, to differentiate them from other volleys;
Total points won and total points shown in the MatchStats tab;
Options to handle certain now-rare match formats, such as tiebreaks at 8-all (as in some 1970s Wimbledons) and matches with no tiebreaks at all.

If you’re already an experienced contributor, just click here to download the new version. Take a quick look through the Instructions tab, as I’ve highlighted the relevant changes.

If you’re new to the MCP, please take a look at my Quick Start Guide, after which you can give the new template a spin.

The Last 156 Men’s Grand Slam Finals

I’m proud to report a big new milestone for the Match Charting Project! We’ve completed the set of men’s Grand Slam finals back to 1980, something that I’ve aspired to since the early days of the project, and a project that has drawn on a lot of effort from many contributors to the project, especially Edo, who is responsible for a huge part of this accomplishment.

Here’s the complete list of charted slam finals, with links to the shot-by-shot data for each match.

From 1980 to this year’s Australian Open, that’s 152 consecutive men’s finals. I went on a bit of a spree last week, which extended the set back to 1979 and upped the total to 156. We’ve got a few earlier slam finals in the database as well, though there’s a limit to how much more we’ll be able to achieve: Before the late 1970s, video quality and availability decreases sharply.

For researchers, as well as those interested in tennis history, this is valuable stuff, made even more useful by its completeness. With the exception of a handful of missing points here and there, the Match Charting Project now includes a wealth of data for the entirety of all of these matches: serve direction, shot types, strategic choices (like serve-and-volleying), and much more, all in a standard format.

It’s particularly satisfying the check off the last few items on a list. (In this case, the final missing pieces were 1987 Roland Garros and the 1981 Australian Open.) Even though 156 matches is a small fraction of the nearly 4,000 contests tracked as part of the MCP, the subset’s completeness means that we can study it without worrying about the non-random nature of video availability and fan interest. If you want to look into, for instance, how net play has changed at Wimbledon over the last four decades, we’ve got the entire run.

In that vein, we are working on several other noteworthy subsets: Masters 1000 finals, 2018 tour-level finals, meetings between members of the big four, and finals played by members of the big four, among others.

We’re getting close to the complete run of women’s slam finals, as well. We’re up to 137 of the 152 since 1980, and have them all from 1999-present. We haven’t been able to find video for the rest, most notably the 1998 US Open (Davenport-Hingis), 1994 Roland Garros (Graf-Pierce), 1994 US Open (Sanchez-Graf), and 1991 Australian Open (Seles-Novotna). The complete list is here, and the remainder date from 1980-86. If you can help us find any of these, please let me know!

As always, if you find this project interesting, please contribute. Our 2.3 million shots worth of detailed data didn’t appear by magic–we rely on volunteers to chart matches, and I hope you’ll join our ranks. Here’s why I think you should, and here’s how you can get started.

The Most Aggressive ATP Returners

In yesterday’s post, I outlined a new method to measure return aggression. Using Aggression Score (AS) as a starting point, I made some adjustments in order to treat return winners (and induced forced errors) and return errors separately. The resulting metric–Return Aggression Score (RAS)–gives equal weight to return winners and return errors. A positive RAS represents an aggressive return game, while a negative number indicates a more conservative one. The most aggressive single-match performances were nearly four standard deviations above the mean, while player averages varied between about one standard deviation above and below the mean.

We can now point the algorithm at the ATP, and calculate RAS for each player in the 1,500 or so 2010-present men’s matches logged by the Match Charting Project.

The difference between the frequency of return errors and return winners is even greater for men than it is for women. The WTA tour averages, as we saw yesterday, are 17.8% and 5.5%, respectively, and the men’s averages are 20.9% and 4.1%. Thus, treating the two categories separately is even more important when analyzing ATP matches.

The overall range in single-match RAS figures is about the same as it is for women. The most aggressive one-match returners are nearly four standard deviations above the mean (a RAS mark near 4.0), while the lowest are almost two standard deviations below (RAS marks near -2.0). What differs between genders is that the most aggressive men’s single-match performances are not clustered around one player, as Serena Williams dominates the women’s list. Of the top ten one-match men’s RAS marks, only one player appears twice, and that is partly an accident:

Year  Event         Returner      Opponent   RAS  
2015  Halle         Berdych       Karlovic  3.96  
2014  Halle         D Brown       Nadal     3.72  
2016  Stuttgart     Marchenko     Groth     3.49  
2014  Aus Open      Dolgopolov    Berankis  2.99  
2016  Dallas CH     Tiafoe        Groth     2.91  
2014  Bogota        J Wang        Karlovic  2.79  
2015  Fairfield CH  Tiafoe        D Brown   2.72  
2017  Montpellier   De Schepper   M Zverev  2.64  
2015  Madrid        Isner         Kyrgios   2.60  
2014  Halle         An Kuznetsov  D Brown   2.58

Two factors make it more likely a returner appears on this list: His opponent, and the surface. Facing a serve-and-volleyer means adopting a higher-risk return strategy, and playing on a faster surface has a similar effect. Four of the top ten matches here were played on grass, and seven of the ten returners faced opponents who often come in behind their serves. Frances Tiafoe is partly responsible for his double-appearance here, but I suspect it has more to do with his opponents.

Grass is, by far, the most extreme surface in its effect on return tactics. Here are the numbers for each court type, along with the RAS of the average match on that surface:

Surface  RetE%  RetW%    RAS  
Hard     21.4%   4.1%   0.04  
Grass    25.3%   5.6%   0.54  
Clay     18.5%   3.5%  -0.24  
Average  20.9%   4.1%   0.00

Even though the average clay court match isn’t as extreme as a grass court match in this regard, the ten least aggressive single-match return performances all took place on clay, five of them recorded by Rafael Nadal.

Player averages

The Match Charting Project has at least 10 matches (2010-present) for about 75 players. Here is the top quintile, the 15 most aggressive players of that group:

Player                 Matches  RetPts   RAS  
Dustin Brown                11     676  1.90  
Ivo Karlovic                16    1116  0.85  
John Isner                  30    2202  0.77  
Alexandr Dolgopolov         20    1417  0.76  
Philipp Kohlschreiber       18    1334  0.69  
Lukas Rosol                 11     841  0.67  
Vasek Pospisil              14     812  0.62  
Andrey Kuznetsov            11     585  0.54  
Benoit Paire                17    1198  0.54  
Jeremy Chardy               14     923  0.39  
Kevin Anderson              23    1681  0.39  
Kei Nishikori               47    3128  0.38  
Milos Raonic                42    3211  0.34  
Sam Querrey                 17    1219  0.31  
Fernando Verdasco           17    1109  0.30

There’s aggression, and then there’s Dustin Brown. No other player is one full standard deviation above average, and he is nearly two, more than twice as aggressive as the next-most tactically extreme ATPer.

We don’t see quite the same extremes in the other direction, just a bunch of clay-courters:

Player                  Matches  RetPts    RAS  
Jiri Vesely                  11     716  -0.76  
Marcel Granollers            12     746  -0.64  
Paolo Lorenzi                13     912  -0.58  
Inigo Cervantes Huegun       10     705  -0.58  
Tommy Robredo                10     622  -0.57  
Damir Dzumhur                11     688  -0.56  
Guido Pella                  11     749  -0.51  
Guillermo Garcia Lopez       10     734  -0.49  
Casper Ruud                  16    1000  -0.48  
Hyeon Chung                  10     621  -0.48  
Rafael Nadal                157   11773  -0.42  
Richard Gasquet              36    2180  -0.42  
Roberto Bautista Agut        25    1633  -0.42  
Diego Schwartzman            44    3289  -0.42  
Juan Martin Del Potro        42    2900  -0.40

These least-aggressive numbers are partly a reflection of playing styles, and partly the surface, as we’ve already seen.

Next, let’s look at how much players alter their style to the circumstances. Here are 16 players–top guys along with some others I found interesting–along with their average RAS numbers on the three major surfaces:

Player                   RAS   Hard   Clay  Grass  
John Isner              0.77   0.71   1.03   0.72  
Marin Cilic             0.28   0.09   0.02   1.38  
Jo Wilfried Tsonga      0.24   0.31  -0.22   0.38  
Gilles Muller           0.10   0.07  -0.74   1.13  
Roger Federer           0.08   0.04  -0.07   0.40  
Grigor Dimitrov         0.07   0.12  -0.30   0.28  
Novak Djokovic          0.02   0.03  -0.12   0.25  
Nick Kyrgios            0.02  -0.06   0.07   1.20  
Jack Sock              -0.08  -0.09   0.08         
Stanislas Wawrinka     -0.09  -0.11  -0.23   0.95  
Alexander Zverev       -0.13  -0.06  -0.33   0.18  
Andy Murray            -0.20  -0.25  -0.32   0.15  
Dominic Thiem          -0.24  -0.13  -0.40   0.25  
Juan Martin Del Potro  -0.40  -0.43  -0.58  -0.07  
Diego Schwartzman      -0.42  -0.34  -0.45         
Rafael Nadal           -0.42  -0.25  -0.76   0.57

The big servers have some surprises in store: John Isner is more aggressive on the return on clay than on other surfaces, and Jack Sock and Nick Kyrgios show the same, at least compared to hard courts. Marin Cilic is extremely aggressive on the grass court return, but his clay court tactics are similar to those on hard courts. In stark contrast is Gilles Muller, second only to Nadal as a conservative returner on clay, but quite aggressive on other surfaces.

One of the many underexplored topics in tennis analytics is the different ways players change (or choose not to change) their tactics on different surfaces. While comparing Return Aggression Score by surface is a tiny step in that direction, it does suggest just how much those strategies vary.

As always, a reminder that analyses like these are only possible with the volunteer-generated shot-by-shot logs of the Match Charting Project. I hope you’ll contribute.

Measuring Return Aggression

In the last couple of years, I’ve gotten a lot of mileage out of a metric called Aggression Score (AS), first outlined here by Lowell West. The stat is so useful due to its simplicity. The more aggressive a player is, the more she’ll rack up both winners and unforced errors. AS, then, is essentially the rate at which a player hits winners and unforced errors.

Yet one limitation lies in Aggression Score’s simplicity. It works best when winners and unforced errors move together, and when they are roughly similar. If someone is having a really bad day, her unforced errors might skyrocket, resulting in a higher AS, even if the root cause of the errors is poor play, not aggression. On the flip side, a locked-in player will see her AS increase by hitting more winners, even if those winners are more a reflection of good form than a high-risk tactic.

I’ve long wanted to extend the idea behind Aggression Score to return tactics, but when we narrow our view to the second shot of the rally, the simplicity of the metric becomes a handicap. On the return, the vast majority of “aggressive” shots are errors, so the results will be swamped by error rate, minimizing the role of return winners, which are a more reliable indicator. Using Match Charting Project data from 2010-present women’s tennis, returns result in errors 18% of the time, while they turn into winners (or they induce forced errors) less than one-third as often, 5.5% of the time. The appealingly simple Aggression Score formula, narrowed to consider only returns of serve, won’t do the job here.

Return aggression score

Let’s walk through a formula to measure return aggression, using last month’s Miami final between Sloane Stephens and Jelena Ostapenko as an example. Tallying up return points (excluding aces and service winners), along with return errors* and return winners** for both players from the match chart, we get the following:

Returner          RetPts  RetErr  RetWin  RetE%  RetW%  
Sloane Stephens       64       9       1  14.1%   1.6%  
Jelena Ostapenko      63      11       6  17.5%   9.5%

* “errors” are a combination of forced and unforced, because most return errors are scored as forced errors, and because the distinction between the two is so unreliable as to be meaningless. Some forced error returns are nearly impossible to make, so they don’t really belong in this analysis, but with the state of available data, it’ll have to do.

** throughout this post, I’ll use “winners” as short-hand for “winners plus induced forced errors” — that is, shots that were good enough to end the point.

These numbers make clear which of the two players is the aggressive one, and they confirm the obvious: Ostapenko plays much higher-risk tennis than Stephens does. In this case, Ostapenko’s rates are nearly equal to or above the tour averages of 17.8% and 5.5%, while both of Stephens’s are well below them.

The next step is to normalize the error and winner rates so that we can more easily see how they relate to each other. To do that, I simply divide each number by the tour average:

Returner          RetE%  RetW%  RetE+  RetW+  
Sloane Stephens   14.1%   1.6%   0.79   0.28  
Jelena Ostapenko  17.5%   9.5%   0.98   1.73

The last two columns show the normalized figures, which reflect how each rate compares to tour average, where 1.0 is average, greater than 1 means more aggressive, and less than 1 means less aggressive.

We’re not quite done yet, because, as Ostapenko and Stephens illustrate, return winner rates are much noisier than return error rates. That’s largely a function of how few there are. The gap between the two players’ normalized rates, 0.28 and 1.73, looks huge, but represents a difference of only five winners. If we leave return winner rates untouched, we’ll end up with a metric that varies largely due to movement in winner rates–the opposite problem from where we started.

To put winners and errors on a more equal footing, we can express both in terms of standard deviations. The standard deviation of the adjusted error ratio is 0.404, while the standard deviation of the adjusted winner ratio is 0.768, so when we divide the ratios by the standard deviations, we’re essentially reducing the variance in the winner number by half. The resulting numbers tell us how many standard deviations a certain statistic is above or below the mean, and these final results give us winner and error rates that are finally comparable to each other:

Returner          RetE+  RetW+  RetE-SD  RetW-SD  
Sloane Stephens    0.79   0.28    -0.52    -0.93  
Jelena Ostapenko   0.98   1.73    -0.05     0.95

(Math-oriented readers might notice that the last two steps don’t need to be separate; we could just as easily think of these last two numbers as standard deviations above or below the mean of the original winner and error rates. I included the intermediate step to–I hope–make the process a bit more intuitive.)

Our final stat, Return Aggression Score (RAS) is simply the average of those two rates measured in standard deviations:

Returner          RetE-SD  RetW-SD    RAS  
Sloane Stephens     -0.52    -0.93  -0.73  
Jelena Ostapenko    -0.05     0.95   0.45

Positive numbers represent more aggression than tour average; negative numbers less aggression. Ostapenko’s +0.45 figure is higher than about 75% of player-matches among the nearly 4,000 in the Match Charting Project dataset, though as we’ll see, it is far more conservative than her typical strategy. Stephens’s -0.73 mark is at the opposite position on the spectrum, higher than only one-quarter of player-matches. It is also lower than her own average, though it is higher than the -0.97 RAS she posted in the US Open final last fall.

The extremes

The first test of any new metric is whether the results actually make sense, and we need look no further than the top ten most aggressive player-matches for confirmation. Five of the top ten most aggressive single-match return performances belong to Serena Williams, and the overall most aggressive match is Serena’s 2013 Roland Garros semifinal against Sara Errani, which rates at 3.63–well over three standard deviations above the mean. The other players represented in the top ten are Ostapenko, Oceane Dodin, Petra Kvitova, Madison Keys, and Julia Goerges–a who’s who of high-risk returning in women’s tennis.

The opposite end of the spectrum includes another group of predictable names, such as Simona Halep, Agnieszka Radwanska, Caroline Wozniacki, Annika Beck, and Errani. Two of Halep’s early matches are lowest and third-lowest, including the 2012 Brussels final against Radwanska, in which her return aggression was 1.6 standard deviations below the mean. It’s not as extreme a mark as Serena’s performances, but that’s the nature of the metric: Halep returned 46 of 48 non-ace serves, and none of the 46 returns went for winners. It’s tough to be less aggressive than that.

The leaderboard

The Match Charting Project has shot-by-shot data on at least ten matches each for over 100 WTA players. Of those, here are the top ten, as ranked by RAS:

Player                    Matches  RetPts   RAS  
Oceane Dodin                   11     665  1.18  
Aryna Sabalenka                11     816  1.12  
Camila Giorgi                  19    1155  1.07  
Mirjana Lucic                  11     707  1.05  
Julia Goerges                  27    1715  0.94  
Petra Kvitova                  65    4142  0.90  
Serena Williams                91    5593  0.90  
Jelena Ostapenko               35    2522  0.88  
Anastasia Pavlyuchenkova       21    1180  0.78  
Lucie Safarova                 34    2294  0.77

We’ve already seen some of these names, in our discussion of the highest single-match marks. When we average across contests, a few more players turn up with RAS marks over one full standard deviation above the mean: Aryna Sabalenka, Camila Giorgi, and Mirjana Lucic-Baroni.

Again, the more conservative players don’t look as extreme: Only Madison Brengle has a RAS more than one standard deviation below the mean. I’ve included the top 20 on this list because so many notable names (Wozniacki, Radwanska, Kerber) are between 11 and 20:

Player                Matches  RetPts     RAS  
Madison Brengle            11     702   -1.06  
Monica Niculescu           32    2099   -0.93  
Stefanie Voegele           12     855   -0.85  
Annika Beck                16    1181   -0.78  
Lara Arruabarrena          10     627   -0.72  
Johanna Larsson            14     873   -0.65  
Barbora Strycova           20    1275   -0.63  
Sara Errani                25    1546   -0.60  
Carla Suarez Navarro       36    2585   -0.55  
Svetlana Kuznetsova        27    2271   -0.55 

Player                Matches  RetPts     RAS  
Viktorija Golubic          16    1272   -0.53  
Agnieszka Radwanska        96    6239   -0.51  
Yulia Putintseva           22    1552   -0.51  
Caroline Wozniacki         80    5165   -0.50  
Christina McHale           11     763   -0.48  
Angelique Kerber           93    6611   -0.46  
Louisa Chirico             13     806   -0.44  
Darya Kasatkina            26    1586   -0.43  
Magdalena Rybarikova       12     725   -0.41  
Anastasija Sevastova       30    1952   -0.40

A few more notable names: Halep, Stephens and Elina Svitolina all count among the next ten lowest, with RAS figures between -0.30 and -0.36. The most “average” player among game’s best is Victoria Azarenka, who rates at -0.08. Venus Williams, Johanna Konta, and Garbine Muguruza make up a notable group of aggressive-but-not-really-aggressive women between +0.15 and +0.20, just outside of the game’s top third, while Maria Sharapova, at +0.63, misses our first list by only a few places.

Unsurprisingly, these results track quite closely to overall Aggression Score figures, as players who adopt a high-risk strategy overall are probably doing the same when facing the serve. This metric, however, allows to identify players–or even single matches–for which the two strategies don’t move in concert. Further, the approach I’ve taken here, to separate and normalize winners and errors, rather than treat them as an undifferentiated mass, could be applied to Aggression Score itself, or to other more targeted versions of the metric, such as a third-shot AS, or a backhand-specific AS.

As always, the more data we have, the more we can learn from it. Analyses like these are only possible with the work of the volunteers who have contributed to the Match Charting Project. Please help us continue to expand our coverage and give analysts the opportunity to look at shot-by-shot data, instead of just the basics published by tennis’s official federations.

Measuring the Best Smashes in Tennis

Italian translation at settesei.it: part 1, part 2

How can we identify the best shots in tennis? At first glance, it seems like a simple problem. Thanks to the shot-by-shot data collected for over 3,500 matches by the Match Charting Project, we can look at every instance of the shot in question and see what happened. If a player hits a lot of winners, or wins most of the ensuing points, he or she is probably pretty good at that shot. Lots of unforced errors would lead us to conclude the opposite.

A friend recently posed a more specific question: Who has the best smash in the men’s game? Compared to other shots such as, say, slice backhands, smashes should be pretty easy to evaluate. A large percentage of them end the point–in the contemporary men’s game (I discuss the women’s game later on), 69% are winners or induce forced errors–which reduces the problem to a straightforward one.

The simplest algorithm to answer my friend’s question is to determine how often each player ends the point in his favor when hitting a smash–that is, with a winner or by inducing a forced error. Call the resulting ratio “W/SM.” The Match Charting Project (MCP) dataset has at least 10 tour-level matches for 80 different men, and the W/SM ratio for those players ranges from 84% (Jeremy Chardy) all the way down to 30% (Paolo Lorenzi). Both of those extremes are represented by players with relatively small samples; if we limit our scope to men with at least 90 recorded smashes, the range isn’t quite as wide. The best of the bunch is Jo-Wilfried Tsonga, at 79%, and the “worst” is Ivan Lendl, at 57%. That isn’t quite fair to Lendl, since smash success rates have improved quite a bit over the years, and Lendl’s rate is only a couple percentage points below the average for the 1980s. Among active players with at least 90 smashes in the books, Stan Wawrinka brings up the rear, with a W/SM of 65%.

We can look at the longer-term effects of a player’s smashes without adding much complexity. It’s ideal to end the point with a smash, but most players would settle for winning the point. When hitting a smash, ATPers these days end up winning the point 81% of the time, ranging from 97% (Chardy again) down to 45% (Lorenzi again). Once again, Tsonga leads the pack of the bigger-sample-size players, winning the point 90% of the time after hitting a smash, and among active players, Wawrinka is still at the bottom of that subset, at 77%.

Here is a list of all players with at least 90 smashes in the MCP dataset, with their winners (and induced forced errors) per smash (W/SM), errors per smash (E/SM), and points won per smash (PTS/SM):

PLAYER              W/SM  E/SM  PTS/SM  
Jo-Wilfried Tsonga   78%    6%     90%  
Tomas Berdych        76%    6%     88%  
Pete Sampras         75%    7%     86%  
Roger Federer        73%    7%     86%  
Rafael Nadal         69%    7%     84%  
Milos Raonic         73%    9%     82%  
Andy Murray          67%    6%     82%  
Kei Nishikori        68%   11%     81%  
David Ferrer         71%    9%     81%  
Andre Agassi         67%    8%     80%  
Novak Djokovic       66%    9%     80%  
Stefan Edberg        62%   12%     78%  
Stan Wawrinka        65%   10%     77%  
Ivan Lendl           57%   13%     71%

These numbers give us a pretty good idea of who you should back if the ATP ever hosts the smash-hitting equivalent of baseball’s Home Run Derby. Best of all, it doesn’t commit any egregious offenses against common sense: We’d expect to see Tsonga and Roger Federer near the top, and we’d know something was wrong if Novak Djokovic were too far from the bottom.

Smash opportunities

Still, we need to do better. Almost every shot made in a tennis match represents a decision made by the player hitting it: topspin or slice? backhand or run-around forehand? approach or stay back? Many smashes are obvious choices, but a large number are not. Different players make different choices, and to evaluate any particular shot, we need to subtly reframe the question. Instead of vaguely asking for “the best,” we’d be better served looking for the player who gets the most value out of his smash. While the two questions are similar, they are not the same.

Let’s expand our view to what we might call “smash opportunities.” Once again, smashes make our task relatively straightforward: We can define a smash opportunity simply as a lob hit by the opponent.* In the contemporary ATP, roughly 72% of lobs result in smashes–the rest either go for winners or are handled with a different shot. Different players have very different strategies: Federer, Pete Sampras, and Milos Raonic all hit smashes in more than 84% of opportunities, while a few other men come in under 50%. Nick Kyrgios, for instance, tried a smash in only 20 of 49 (41%) of recorded opportunities. Of those players with more available data, Juan Martin Del Potro elected to go for the overhead in 61 of 114 (54%) of chances, and Andy Murray in 271 of 433 (62.6%).

* Using an imperfect dataset, it’s a bit more complicated; sometimes the shots that precede smashes are coded as topspin or slice groundstrokes. I’ve counted those as smash opportunities as well.

Not all lobs are created equal, of course. With a large number of points, we would expect them to even out, but even then, a player’s overall style may effect the smash opportunities he sees. That’s a more difficult issue for another day; for now, it’s easiest to assume that each player’s mix of smash opportunities are roughly equal, though we’ll keep in mind the likelihood that we’ve swept some complexity under the rug.

With such a wide range of smashes per smash opportunities (SM/SMO), it’s clear that some players’ average smashes are more difficult than others. Federer hits about half again as many smashes per opportunity as del Potro does, suggesting that Fed’s attempts are more difficult than Delpo’s; on those more difficult attempts, Delpo is choosing a different shot. The Argentine is very effective when he opts for the smash, winning 84% of those points, but it seems likely that his rate would not be so high if he hit smashes as frequently as Federer does.

This leads us to a slightly different question: Which players are most effective when dealing with smash opportunities? The smash itself doesn’t necessarily matter–if a player is equally effective with, say, swinging volleys, the lack of a smash would be irrelevant. The smash is simply an effective tool that most players employ to deal with these situations.

Smash opportunities don’t offer the same level of guarantee that smashes themselves do: In the ATP these days, players win 72% of points after being handed a smash opportunity, and 56% of the shots they hit result in winners or induced forced errors. Looking at these situations takes us a bit off-track, but it also allows us to study a broader question with more impact on the game as a whole, because smash opportunities represent a larger number of shots than smashes themselves do.

Here is a list of all the players with at least 99 smash opportunities in the MCP dataset, along with the rate at which they hit smashes (SM/SMO), the rate at which they hit winners or induced forced errors in response to smash opportunites (W/SMO), hit errors in those situations (E/SMO), and won the points when given lobs (PTW/SMO). Like the list above, players are ranked by the rightmost column, points won.

PLAYER              SM/SMO  W/SMO  E/SMO  PTW/SMO  
Jo-Wilfried Tsonga     80%    68%    13%      80%  
Roger Federer          84%    66%    13%      78%  
Pete Sampras           86%    68%    15%      78%  
Tomas Berdych          75%    66%    16%      76%  
Milos Raonic           85%    67%    14%      76%  
Novak Djokovic         81%    60%    13%      75%  
Kevin Anderson         66%    57%    12%      74%  
Rafael Nadal           74%    57%    16%      73%  
Andre Agassi           77%    62%    17%      73%  
Boris Becker           85%    59%    18%      72%  
Stan Wawrinka          79%    58%    15%      72%  
Kei Nishikori          72%    57%    17%      70%  
Andy Murray            63%    52%    15%      70%  
Dominic Thiem          66%    52%    11%      70%  
David Ferrer           71%    57%    17%      69%  
Pablo Cuevas           73%    54%    14%      67%  
Stefan Edberg          81%    52%    23%      65%  
Bjorn Borg             81%    41%    20%      63%  
JM del Potro           54%    48%    19%      60%  
Ivan Lendl             74%    45%    28%      59%  
John McEnroe           74%    43%    24%      56%

The order of this list has much in common with the previous one, with names like Federer, Sampras, and Tsonga at the top. Yet there are key differences: Djokovic and Wawrinka are particularly effective when they respond to a lob with something other than an overhead, while del Potro is the opposite, landing near the bottom of this ranking despite being quite effective with the smash itself.

The rate at which a player converts opportunities to smashes has some impact on his overall success rate on smash opportunities, but the relationship isn’t that strong (r^2 = 0.18). Other options, such as swinging volleys or mid-court forehands, also give players a good chance of winning the point.

Smash value

Let’s get back to my revised question: Who gets the most value out of his smash? A good answer needs to combine how well he hits it with how often he hits it. Once we can quantify that, we’ll be able to see just how much a good or bad smash can impact a player’s bottom line, measured in overall points won, and how much a great smash differs from an abysmal one.

As noted above, the average current-day ATPer wins the point 81% of the time that he hits a smash. Let’s reframe that in terms of the probability of winning a point: When a lob is flying through the air and a player readies his racket to hit an overhead, his chance of winning the point is 81%–most of the hard work is already done, having generated such a favorable situation. If our player ends up winning the point, the smash improved his odds by 0.19 points (from 0.81 to 1.0), and if he ends up losing the point, the smash hurt his odds by 0.81 (from 0.81 to 0.0). A player who hits five successful smashes in a row has a smash worth about one total point: 5 multiplied by 0.19 equals 0.95.

We can use this simple formula to estimate how much each player’s smash is worth, denominated in points. We’ll call that Point Probability Added (PPA). Finally, we need to take into account how often the player hits his smash. To do so, we’ll simply divide PPA by total number of points played, then multiply by 100 to make the results more readable. The metric, then, is PPA per 100 points, reflecting the impact of the smash in a typical short match. Most players have similar numbers of smash opportunities, but as we’ve seen, some choose to hit far more overheads than others. When we divide by points, we give more credit to players who hit their smashes more often.

The overall impact of the smash turns out to be quite small. Here are the 1990s-and-later players with at least 99 smash opportunities in the dataset along with their smash PPA per 100 points:

PLAYER                 SM PPA/100  
Jo-Wilfried Tsonga           0.17  
Pete Sampras                 0.11  
Tomas Berdych                0.11  
Roger Federer                0.10  
Rafael Nadal                 0.05  
Milos Raonic                 0.04  
Juan Martin del Potro        0.02  
Andy Murray                  0.01  
Kevin Anderson               0.01  
Kei Nishikori                0.00  
David Ferrer                 0.00  
Andre Agassi                 0.00  
Novak Djokovic              -0.02  
Stan Wawrinka               -0.07  
Dominic Thiem               -0.07  
Pablo Cuevas                -0.10

Tsonga reigns supreme, from the most basic measurement to the most complex. His 0.17 smash PPA per 100 points means that the quality of his overhead earns him about one extra point (compared to an average ATPer) every 600 points. That doesn’t sound like much, and rightfully so: He hits fewer than one smash per 50 points, and as good as Tsonga is, the average player has a very serviceable smash as well.

The list gives us an idea of the overall range of smash-hitting ability, as well. Among active players, the laggard in this group is Pablo Cuevas, at -0.1 points per 100, meaning that his subpar smash costs him one point out of every thousand he plays. It’s possible to be worse–in Lorenzi’s small sample, his rate is -0.65–but if we limit our scope to these well-studied players, the difference between the high and low extremes is barely 0.25 points per 100, or one point out of every 400.

I’ve excluded several players from earlier generations from this list; as mentioned earlier, the average smash success rate in those days was lower, so measuring legends like McEnroe and Borg using a 2010s-based point probability formula is flat-out wrong. That said, we’re on safe ground with Sampras and Agassi; the rate at which players convert smashes into points won has remained fairly steady since the early 1990s.

Lob-responding value

We’ve seen the potential impact of smash skill; let’s widen our scope again and look at the potential impact of smash opportunity skill. When a player is faced with a lob, but before he decides what shot to hit, his chance of winning the point is about 72%. Thus, hitting a shot that results in winning the point is worth 0.28 points of point probability added, while a choice that ends up losing the point translates to -0.72.

There are more smash opportunities than smashes, and more room to improve on the average (72% instead of 81%), so we would expect to see a bigger range of PPA per 100 points. Put another way, we would expect that lob-responding skill, which includes smashes, is more important than smash-specific skill.

It’s a modest difference, but it does look like lob-responding skill has a bigger range than smash skill. Here is the same group of players, still showing their PPA/100 for smashes (SM PPA/100), now also including their PPA/100 for smash opportunities (SMO PPA/100):

PLAYER                 SM PPA/100  SMO PPA/100  
Jo-Wilfried Tsonga           0.17         0.18  
Roger Federer                0.10         0.16  
Pete Sampras                 0.11         0.16  
Milos Raonic                 0.04         0.12  
Tomas Berdych                0.11         0.09  
Kevin Anderson               0.01         0.08  
Novak Djokovic              -0.02         0.07  
Rafael Nadal                 0.05         0.03  
Andre Agassi                 0.00         0.01  
Stan Wawrinka               -0.07         0.00  
Kei Nishikori                0.00        -0.03  
Andy Murray                  0.01        -0.03  
Dominic Thiem               -0.07        -0.05  
David Ferrer                 0.00        -0.06  
Pablo Cuevas                -0.10        -0.12  
Juan Martin del Potro        0.02        -0.19

Djokovic and Delpo draw our attention again as the players whose smash skills do not accurately represent their smash opportunity skills. Djokovic is slightly below average with smashes, but a few notches above the norm on opportunities; Delpo is a tick above average when he hits smashes, but dreadful when dealing with lobs in general.

As it turns out, we can measure the best smashes in tennis, both to compare players and to get a general sense of the shot’s importance. What we’ve also seen is that smashes don’t tell the entire story–we learn more about a player’s overall ability when we widen our view to smash opportunities.

Smashes in the women’s game

Contemporary women hit far fewer smashes than men do, and they win points less often when they hit them. Despite the differences, the reasoning outlined above applies just as well to the WTA. Let’s take a look.

In the WTA of this decade, smashes result in winners (or induced forced errors) 63% of the time, and smashes result in points won about 75% of the time. Both numbers are lower than the equivalent ATP figures (69% and 81%, respectively), but not dramatically so. Here are the rates of winners, errors, and points won per smash for the 14 women with at least 80 smashes in the MCP dataset:

PLAYER               W/SM  E/SM  PTS/SM  
Jelena Jankovic       73%    9%     83%  
Serena Williams       72%   13%     81%  
Steffi Graf           61%    9%     81%  
Svetlana Kuznetsova   70%   10%     79%  
Simona Halep          66%   11%     76%  
Caroline Wozniacki    61%   16%     74%  
Karolina Pliskova     62%   18%     74%  
Agnieszka Radwanska   54%   13%     74%  
Angelique Kerber      57%   15%     72%  
Martina Navratilova   54%   13%     71%  
Monica Niculescu      50%   15%     70%  
Garbine Muguruza      63%   19%     70%  
Petra Kvitova         59%   22%     68%  
Roberta Vinci         58%   14%     68%

Historical shot-by-shot data is less representative for women than for men, so it’s probably safest to assume that trends in smash success rates are similar for men than for women. If that’s true, Steffi Graf’s era is similar to the present, while Martina Navratilova’s prime saw far fewer smashes going for winners or points won.

Where the women’s game really differs from the men’s is the difference between smash opportunities (lobs) and smashes. As we saw above, 72% of ATP smash opportunities result in smashes. In the current WTA, the corresponding figure is less than half that: 35%. Some of the single-player numbers are almost too extreme to be believed: In 12 matches, Catherine Bellis faced 41 lobs and hit 3 smashes; in 29 charted matches, Jelena Ostapenko saw 103 smash opportunities and tried only 10 smashes. A generation ago, the gender difference was tiny: Graf, Martina Hingis, Arantxa Sanchez Vicario, and Monica Seles all hit smashes in at least three-quarters of their opportunities. But among active players, only Barbora Strycova comes in above 70%.

Here are the smash opportunity numbers for the 17 women with at least 150 smash opportunities in the MCP dataset. SM/SMO is smashes per chance, W/SMO is winners (and induced forced errors) per smash opportunity, E/SMO is errors per opportunity, and PTS/SMO is points won per smash opportunity:

PLAYER                SM/SMO  W/SMO  E/SMO  PTW/SMO  
Maria Sharapova          12%    57%    11%      76%  
Serena Williams          55%    58%    18%      72%  
Steffi Graf              82%    52%    17%      71%  
Karolina Pliskova        47%    52%    16%      70%  
Simona Halep             14%    41%    11%      69%  
Carla Suarez Navarro     25%    33%     9%      69%  
Eugenie Bouchard         29%    50%    18%      68%  
Victoria Azarenka        35%    52%    17%      67%  
Angelique Kerber         39%    42%    14%      66%  
Garbine Muguruza         43%    51%    18%      66%  
Monica Niculescu         57%    41%    19%      65%  
Petra Kvitova            48%    50%    19%      65%  
Agnieszka Radwanska      44%    42%    18%      65%  
Johanna Konta            30%    47%    21%      64%  
Caroline Wozniacki       36%    44%    18%      64%  
Elina Svitolina          14%    38%    14%      63%  
Martina Navratilova      67%    42%    26%      58%

It’s clear from the top of this list that women’s tennis is a different ballgame. Maria Sharapova almost never opts for an overhead, but when faced with a lob, she is the best of them all. Next up is Serena Williams, who hits almost as many smashes as any active player on this list, and is nearly as successful. Recall that in the men’s game, there is a modest positive correlation between smashes per opportunity and points won per smash opportunity; here, the relationship is weaker, and slightly negative.

Because most women hit so few smashes, there isn’t quite as much to be gained by using point probability added (PPA) to measure WTA smash skill. Graf was exceptionally good, comparable to Tsonga in the value she extracted from her smash, but among active players, only Serena and Victoria Azarenka can claim a smash that is worth close to one point per thousand. At the other extreme, Monica Niculescu is nearly as bad as Graf was good, suggesting she ought to figure out a way to respond to more smash opportunities with her signature forehand slice.

Here is the same group of women (minus Navratilova, whose era makes PPA comparisons misleading), with their PPA per 100 points for smashes (SM PPA/100) and smash opportunities (SMO PPA/100):

PLAYER                SM PPA/100  SMO PPA/100  
Maria Sharapova             0.03         0.21  
Serena Williams             0.09         0.15  
Steffi Graf                 0.15         0.14  
Karolina Pliskova          -0.01         0.09  
Carla Suarez Navarro        0.04         0.08  
Simona Halep                0.00         0.07  
Eugenie Bouchard           -0.02         0.03  
Victoria Azarenka           0.08         0.00  
Angelique Kerber           -0.03        -0.02  
Garbine Muguruza           -0.07        -0.03  
Petra Kvitova              -0.07        -0.04  
Monica Niculescu           -0.13        -0.06  
Caroline Wozniacki         -0.01        -0.07  
Agnieszka Radwanska        -0.02        -0.07  
Johanna Konta              -0.12        -0.08  
Elina Svitolina             0.01        -0.09

The table is sorted by smash opportunity PPA, which tells us about a much more relevant skill in the women’s game. Sharapova’s lob-responding ability is well ahead of the pack, worth better than one point above average per 500, with Serena and Graf not far behind. The overall range among these well-studied players, from Sharapova’s 0.21 to Elina Svitolina’s -0.09, is somewhat smaller than the equivalent range in the ATP, but with such outliers as Sharapova here and Delpo on the men’s side, it’s tough to draw firm conclusions from small subsets of players, however elite they are.

Final thought

The approach I’ve outlined here to measure the impact of smash and smash-opportunity skills is one that could be applied to other shots. Smashes are a good place to start because they are so simple: Many of them end points, and even when they don’t, they often virtually guarantee that one player will win the point. While smashes are a bit more complex than they first appear, the complications involved in applying a similar algorithm to, say, backhands and backhand opportunities, are considerably greater. That said, I believe this algorithm represents a promising entry point to these more daunting problems.

Measuring the Impact of the Serve in Men’s Tennis

By just about any measure, the serve is the most important shot in tennis. In men’s professional tennis, with its powerful deliveries and short points, the serve is all the more crucial. It is the one shot guaranteed to occur in every rally, and in many points, it is the only shot.

Yet we don’t have a good way of measuring exactly how important it is. It’s easy to determine which players have the best serves–they tend to show up at the top of the leaderboards for aces and service points won–but the available statistics are very limited if we want a more precise picture. The ace stat counts only a subset of those points decided by the serve, and the tally of service points won (or 1st serve points won, or 2nd serve points won) combines the effect of the serve with all of the other shots in a player’s arsenal.

Aces are not the only points in which the serve is decisive, and some service points won are decided long after the serve ceases to have any relevance to the point. What we need is a method to estimate how much impact the serve has on points of various lengths.

It seems like a fair assumption that if a server hits a winner on his second shot, the serve itself deserves some of the credit, even if the returner got it back in play. In any particular instance, the serve might be really important–imagine Roger Federer swatting away a weak return from the service line–or downright counterproductive–think of Rafael Nadal lunging to defend against a good return and hitting a miraculous down-the-line winner. With the wide variety of paths a tennis point can follow, though, all we can do is generalize. And in the aggregate, the serve probably has a lot to do with a 3-shot rally. At the other extreme, a 25-shot rally may start with a great serve or a mediocre one, but by the time by the point is decided, the effect of the serve has been canceled out.

With data from the Match Charting Project, we can quantify the effect. Using about 1,200 tour-level men’s matches from 2000 to the present, I looked at each of the server’s shots grouped by the stage of the rally–that is, his second shot, his third shot, and so on–and calculated how frequently it ended the point. A player’s underlying skills shouldn’t change during a point–his forehand is as good at the end as it is at the beginning, unless fatigue strikes–so if the serve had no effect on the success of subsequent shots, players would end the point equally often with every shot.

Of course, the serve does have an effect, so points won by the server end much more frequently on the few shots just after the serve than they do later on. This graph illustrates how the “point ending rate” changes:

On first serve points (the blue line), if the server has a “makeable” second shot (the third shot of the rally, “3” on the horizontal axis, where “makeable” is defined as a shot that results in an unforced error or is put back in play), there is a 28.1% chance it ends the point in the server’s favor, either with a winner or by inducing an error on the next shot. On the following shot, the rate falls to 25.6%, then 21.8%, and then down into what we’ll call the “base rate” range between 18% and 20%.

The base rate tells us how often players are able to end points in their favor after the serve ceases to provide an advantage. Since the point ending rate stabilizes beginning with the fifth shot (after first serves), we can pinpoint that stage of the rally as the moment–for the average player, anyway–when the serve is no longer an advantage.

As the graph shows, second serve points (shown with a red line) are a very different story. It appears that the serve has no impact once the returner gets the ball back in play. Even that slight blip with the server’s third shot (“5” on the horizontal axis, for the rally’s fifth shot) is no higher than the point ending rate on the 15th shot of first-serve rallies. This tallies with the conclusions of some other research I did six years ago, and it has the added benefit of agreeing with common sense, since ATP servers win only about half of their second serve points.

Of course, some players get plenty of positive after-effects from their second serves: When John Isner hits a second shot on a second-serve point, he finishes the point in his favor 30% of the time, a number that falls to 22% by his fourth shot. His second serve has effects that mirror those of an average player’s first serve.

Removing unforced errors

I wanted to build this metric without resorting to the vagaries of differentiating forced and unforced errors, but it wasn’t to be. The “point-ending” rates shown above include points that ended when the server’s opponent made an unforced error. We can argue about whether, or how much, such errors should be credited to the server, but for our purposes today, the important thing is that unforced errors aren’t affected that much by the stage of the rally.

If we want to isolate the effect of the serve, then, we should remove unforced errors. When we do so, we discover an even sharper effect. The rate at which the server hits winners (or induces forced errors) depends heavily on the stage of the rally. Here’s the same graph as above, only with opponent unforced errors removed:

The two graphs look very similar. Again, the first serve loses its effect around the 9th shot in the rally, and the second serve confers no advantage on later shots in the point. The important difference to notice is the ratio between the peak winner rate and the base rate, which is now just above 10%. When we counted unforced errors, the ratio between peak and base rate was about 3:2. With unforced errors removed, the ratio is close to 2:1, suggesting that when the server hits a winner on his second shot, the serve and the winner contributed roughly equally to the outcome of the point. It seems more appropriate to skip opponent unforced errors when measuring the effect of the serve, and the resulting 2:1 ratio jibes better with my intuition.

Making a metric

Now for the fun part. To narrow our focus, let’s zero in on one particular question: What percentage of service points won can be attributed to the serve? To answer that question, I want to consider only the server’s own efforts. For unreturned serves and unforced errors, we might be tempted to give negative credit to the other player. But for today’s purposes, I want to divvy up the credit among the server’s assets–his serve and his other shots–like separating the contributions of a baseball team’s pitching from its defense.

For unreturned serves, that’s easy. 100% of the credit belongs to the serve.

For second serve points in which the return was put in play, 0% of the credit goes to the serve. As we’ve seen, for the average player, once the return comes back, the server no longer has an advantage.

For first-serve points in which the return was put in play and the server won by his fourth shot, the serve gets some credit, but not all, and the amount of credit depends on how quickly the point ended. The following table shows the exact rates at which players hit winners on each shot, in the “Winner %” column:

Server's…  Winner %  W%/Base  Shot credit  Serve credit  
2nd shot      21.2%     1.96        51.0%         49.0%  
3rd shot      18.1%     1.68        59.6%         40.4%  
4th shot      13.3%     1.23        81.0%         19.0%  
5th+          10.8%     1.00       100.0%          0.0%

Compared to a base rate of 10.8% winners per shot opportunity, we can calculate the approximate value of the serve in points that end on the server’s 2nd, 3rd, and 4th shots. The resulting numbers come out close to round figures, so because these are hardly laws of nature (and the sample of charted matches has its biases), we’ll go with round numbers. We’ll give the serve 50% of the credit when the server needed only two shots, 40% when he needed three shots, and 20% when he needed four shots. After that, the advantage conferred by the serve is usually canceled out, so in longer rallies, the serve gets 0% of the credit.

Tour averages

Finally, we can begin the answer the question, What percentage of service points won can be attributed to the serve? This, I believe, is a good proxy for the slipperier query I started with, How important is the serve?

To do that, we take the same subset of 1,200 or so charted matches, tally the number of unreturned serves and first-serve points that ended with various numbers of shots, and assign credit to the serve based on the multipliers above. Adding up all the credit due to the serve gives us a raw number of “points” that the player won thanks to his serve. When we divide that number by the actual number of service points won, we find out how much of his service success was due to the serve itself. Let’s call the resulting number Serve Impact, or SvI.

Here are the aggregates for the entire tour, as well as for each major surface:

         1st SvI  2nd SvI  Total SvI  
Overall    63.4%    31.0%      53.6%  
Hard       64.6%    31.5%      54.4%  
Clay       56.9%    27.0%      47.8%  
Grass      70.8%    37.3%      61.5%

Bottom line, it appears that just over half of service points won are attributable to the serve itself. As expected, that number is lower on clay and higher on grass.

Since about two-thirds of the points that men win come on their own serves, we can go even one step further: roughly one-third of the points won by a men’s tennis player are due to his serve.

Player by player

These are averages, and the most interesting players rarely hew to the mean. Using the 50/40/20 multipliers, Isner’s SvI is a whopping 70.8% and Diego Schwartzman‘s is a mere 37.7%. As far from the middle as those are, they understate the uniqueness of these players. I hinted above that the same multipliers are not appropriate for everyone; the average player reaps no positive after-effects of his second serve, but Isner certainly does. The standard formula we’ve used so far credits Isner with an outrageous SvI, even without giving him credit for the “second serve plus one” points he racks up.

In other words, to get player-specific results, we need player-specific multipliers. To do that, we start by finding a player-specific base rate, for which we’ll use the winner (and induced forced error) rate for all shots starting with the server’s fifth shot on first-serve points and shots starting with the server’s fourth on second-serve points. Then we check the winner rate on the server’s 2nd, 3rd, and 4th shots on first-serve points and his 2nd and 3rd shots on second-serve points, and if the rate is at least 20% higher than the base rate, we give the player’s serve the corresponding amount of credit.

Here are the resulting multipliers for a quartet of players you might find interesting, with plenty of surprises already:

                   1st serve              2nd serve       
                    2nd shot  3rd  4th     2nd shot  3rd  
Roger Federer            55%  50%  30%           0%   0%  
Rafael Nadal             31%   0%   0%           0%   0%  
John Isner               46%  41%   0%          34%   0%  
Diego Schwartzman        20%  35%   0%           0%  25%  
Average                  50%  30%  20%           0%   0%

Roger Federer gets more positive after-effects from his first serve than average, more even than Isner does. The big American is a tricky case, both because so few of his serves come back and because he is so aggressive at all times, meaning that his base winner rate is very high. At the other extreme, Schwartzman and Rafael Nadal get very little follow-on benefit from their serves. Schwartzman’s multipliers are particularly intriguing, since on both first and second serves, his winner rate on his third shot is higher than on his second shot. Serve plus two, anyone?

Using player-specific multipliers makes Isner’s and Schwartzman’s SvI numbers more extreme. Isner’s ticks up a bit to 72.4% (just behind Ivo Karlovic), while Schwartzman’s drops to 35.0%, the lowest of anyone I’ve looked at. I’ve calculated multipliers and SvI for all 33 players with at least 1,000 tour-level service points in the Match Charting Project database:

Player                 1st SvI  2nd SvI  Total SvI  
Ivo Karlovic             79.2%    56.1%      73.3%  
John Isner               78.3%    54.3%      72.4%  
Andy Roddick             77.8%    51.0%      71.1%  
Feliciano Lopez          83.3%    37.1%      68.9%  
Kevin Anderson           77.7%    42.5%      68.4%  
Milos Raonic             77.4%    36.0%      66.0%  
Marin Cilic              77.1%    34.1%      63.3%  
Nick Kyrgios             70.6%    41.0%      62.5%  
Alexandr Dolgopolov      74.0%    37.8%      61.3%  
Gael Monfils             69.8%    37.7%      60.8%  
Roger Federer            70.6%    32.0%      58.8%  
                                                    
Player                 1st SvI  2nd SvI  Total SvI  
Bernard Tomic            67.6%    28.7%      58.5%  
Tomas Berdych            71.6%    27.0%      57.2%  
Alexander Zverev         65.4%    30.2%      54.9%  
Fernando Verdasco        61.6%    32.9%      54.3%  
Stan Wawrinka            65.4%    33.7%      54.2%  
Lleyton Hewitt           66.7%    32.1%      53.4%  
Juan Martin Del Potro    63.1%    28.2%      53.4%  
Grigor Dimitrov          62.9%    28.6%      53.3%  
Jo Wilfried Tsonga       65.3%    25.9%      52.7%  
Marat Safin              68.4%    22.7%      52.3%  
Andy Murray              63.4%    27.5%      52.0%  
                                                    
Player                 1st SvI  2nd SvI  Total SvI  
Dominic Thiem            60.6%    28.9%      50.8%  
Roberto Bautista Agut    55.9%    32.5%      49.5%  
Pablo Cuevas             57.9%    28.9%      47.8%  
Richard Gasquet          56.0%    29.0%      47.5%  
Novak Djokovic           56.0%    26.8%      47.3%  
Andre Agassi             54.3%    31.4%      47.1%  
Gilles Simon             55.7%    28.4%      46.7%  
Kei Nishikori            52.2%    30.8%      45.2%  
David Ferrer             46.9%    28.2%      41.0%  
Rafael Nadal             42.8%    27.1%      38.8%  
Diego Schwartzman        39.5%    25.8%      35.0%

At the risk of belaboring the point, this table shows just how massive the difference is between the biggest servers and their opposites. Karlovic’s serve accounts for nearly three-quarters of his success on service points, while Schwartzman’s can be credited with barely one-third. Even those numbers don’t tell the whole story: Because Ivo’s game relies so much more on service games than Diego’s does, it means that 54% of Karlovic’s total points won–serve and return–are due to his serve, while only 20% of Schwartzman’s are.

We didn’t need a lengthy analysis to show us that the serve is important in men’s tennis, or that it represents a much bigger chunk of some players’ success than others. But now, instead of asserting a vague truism–the serve is a big deal–we can begin to understand just how much it influences results, and how much weak-serving players need to compensate just to stay even with their more powerful peers.