Jack Sock, Doubles King Once Again

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Italian translation at settesei.it

A couple of years ago, I wrote an article introducing D-Lo, an Elo-like rating system for doubles, which crowned Jack Sock as the best doubles player on the men’s tour. Sock grabbed the top spot in October 2016 and hung on for about nine months, largely by not playing very much. A couple of first-round losses in Washington and Montreal last summer sent him tumbling, landing at 8th after the US Open and as low as 14th going into this year’s Australian Open.

Despite his preference for singles, Sock has rocketed back into the lead, first pairing with John Isner for the Indian Wells title, and then partnering Mike Bryan (replacing injured brother Bob) to win both Wimbledon and the US Open. With the exception of one week immediately after Indian Wells, Sock sits at the head of the D-Lo table for the first time in more than a year. Here are the current top ten, along with their ratings:

Rank  Player                 D-Lo  
1     Jack Sock              1949  
2     Bob Bryan              1930  
3     Mike Bryan             1917  
4     Pierre Hugues Herbert  1906  
5     Nicolas Mahut          1893  
6     Jamie Murray           1886  
7     Bruno Soares           1883  
8     Oliver Marach          1867  
9     Robert Farah           1863  
10    Nikola Mektic          1863

Yes, that’s the injured Bob Bryan in the second spot. More on that in a moment.

A quick refresher on the D-Lo system: It mostly works like a standard Elo algorithm, in that players gain points for winning matches and lose points for losing them, based on the quality of the opponent and the amount of prior information already baked into their ratings. A big upset earns more points than a victory over an equal, and for players with fewer prior matches, the effect of each match is greater. Thus, Sock got a few more points than Mike did for winning the 12 matches at the last two slams, because we knew relatively less about him before those tournaments.

D-Lo assumes that the quality of each team is equal to the average of the two players. If a team wins, each member of the partnership gains points, with one tweak: If the two players have different ratings, their ratings slightly move toward the average of the two. This is because it’s impossible to know how much each player contributes to a win. The system is designed so that, after a year or so of playing together, the two mens’ ratings will meet in the middle. It’s an imperfect system, but it does a reasonably good job of forecasting results, which means it usually provides a solid representation of each player’s skill level.

Back to the matter at hand: Doubles ratings have been particularly volatile this year, with five different men (Sock, Bob, Pierre Hugues Herbert, Mate Pavic, and Henri Kontinen) holding the #1 spot, and two more (Nicolas Mahut and John Peers) peaking at #2. This parity means that no player has a particularly high rating. Two years ago, Sock’s mark of 1949 would have been good for only fourth (behind himself, Herbert, and Mahut), and several players (the Bryans, Herbert, and Daniel Nestor among them) have peaked with ratings above 2000.

Take a look at how much the rank order has fluctuated since the beginning of 2018:

2018 D-Lo leaders

For clarity’s sake, I’ve left off Oliver Marach (whose rating tracks closely with that of his partner, Pavic, and whose season hasn’t lived up to its early promise) and Peers (ditto, with Kontinen). Herbert has reached the highest level of anyone this season, but a rough second half so far has left him behind the American trio of Jack, Bob, and Mike.

Back to the curious case of Bob Bryan. The Bryan brothers’ title at the Madrid Masters this year gave the twins their highest D-Lo ratings in nearly two years. “Standard” Elo doesn’t penalize players for absence, so Bob’s mark has remained at 1930 ever since. (I’ve added an injury/absence penalty in my singles Elo ratings, but haven’t done so for D-Lo. I suspect there is less of an effect, but still a measureable one, in doubles.) Mike’s rating has slipped because of some bad results apart from the pair of majors, and only Sock has caught up.

If Bob is healthy enough to play this fall, the twins are expected to pair up for the World Tour Finals, once again leaving the best doubles player in the world out of the field. In that case, Sock, down to 157th in the ATP singles race, could end up spending that week playing the new ATP Challenger event in Houston. Without their young compatriot in the way, the Bryans will be back in familiar territory, headed to London as the favorites for another year-end title.

Podcast Episode 33: Farewell, Davis Cup World Group Playoffs

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Episode 33 of the Tennis Abstract Podcast features guest host and frequent Heavy Topspin contributor Peter Wetz, who reports from last weekend’s Austria-Australia World Group playoff tie in Graz, which featured Dominic Thiem and podcast favorite Alex de Minaur, among others. We also try to give an explainer of the new Davis Cup format, but it’s possible we’ll leave you more confused than you were before.

Thanks for listening!

(Note: this week’s episode is about 61 minutes long; in some browsers the audio player may display a different length. Sorry about that!)

Click to listen, subscribe on iTunes, or use our feed to get updates on your favorite podcast software.

Update: Episode index with links, thanks to FBITennis:

What’s it like to go to a Davis Cup tie (Austria example)? 1:15
Gunter Bresnik’s coaching legacy 8:15
Dominic Thiem as clay court specialist 10:25
Mr. Sackmann’s One-Hander, and Results 14:20
One-Handed Backhands on Clay 15:40
Who will be #4 next year?  Delpo, Zverev, Murray or Other 16:50
Alex De Minaur 19:20
Other World Group Playoffs Action 28:10
Prediction for 2018 World Cup Final 30:50
New Davis Cup Format/Reforms 36:15
How will the new DC format treat doubles 55:30

The US Open Surface Speed Puzzle

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Italian translation at settesei.it

Almost everyone agrees that the courts were slower at the US Open this year. The players thought so, the media concurred, and the tournament director confirmed that they had slightly changed the physical makeup of the surface in order to slow things down. Even clay-court wizard Dominic Thiem got within two points of the semi-finals, so clearly something changed.

I’m not going to argue with that. But when I set out to measure the change and get a sense of who might have benefited, I kept finding odd results. Almost nothing I tried revealed any clear-cut slowing of the surface, and by some metrics, the courts in Flushing played faster this year. Maybe it was just the heat and humidity–though the numbers don’t make that clear, either.

My usual starting point is my own surface-speed stat, which compares the ace rate at each tournament while controlling for the mix of servers and returners. While the dearth of advanced stats means it is limited to some basic inputs, it usually matches up quite well with our intution and doesn’t differ too much from Court Pace Index (CPI), an infrequently-available metric based on direct physical measurements. Using my algorithm, the US Open surface was 5% faster than the average surface at an ATP event in the last 52 weeks, compared to last year, when it was 4% slower. Compared to courts at the average WTA tournament, New York was 5% slower this year, versus 19% slower in 2017. The slowest tour-level surfaces (for either gender) have about 50% fewer aces than average, and the fastest have about 50% more.

2017 wasn’t just a blip, either in real-life on in my metric. It was similar to 2016, which also rated as considerably slower than this year’s surfaces. We’re left with a discrepancy that may stem from using an algorithm that relies too much on aces: Perhaps players were overwhelmed by the heat and tried more than usual to keep rallies short, or they simply didn’t bother trying to put their racket on first serves as often.

The evidence is clearer that players were more aggressive this year than in 2017. The average rally length, excluding double faults, on courts covered by Slamtracker (179 of the 254 main draw singles matches) fell from 4.28 shots last year to 4.17 this year, a drop of 2.6%. That could be affected by the changing mix of players in the draw (as well as those selected to play on higher-profile courts) so I isolated the 27 players with at least two matches worth of data from both 2017 and 2018. Those 27 saw their rally length drop a tiny bit more, about 3% from last year to this year.

We have the beginnings of an explanation. If players were showing more aggression–perhaps because the heat encouraged them to adopt more first-strike tactics–that could cancel out the effect of a slower surface. We can drill down even further using the Aggression Score (AS) metric, which measures the rate of winners and unforced errors per shot. Across all matches, AS rose from 15.3% in 2017 to 16.1% this year, an increase of 5.7%. Using the 27 players with multiple matches from both years’ tournaments, the difference is more stark, rising by 8.7%.

It’s clear that we saw more aggressive tennis at the 2018 Open than the year before. If we take for granted that the courts played faster, the case is closed: Tactics, probably heat-induced, outweighed surface. But if we approached the problem without knowing what players, media, and tournament officials said, the same numbers would unequivocally point to an even simpler conclusion, that the courts played faster.

If tactics explain our discrepancy, one more place we might look is first serves. Maybe servers took more chances, increasing their ace rate at the expense of first-serve percentage. But the data doesn’t back us up: The overall first-serve percentage in Slamtracker matches fell by a mere 0.07%. Using year-to-year comparisons for our set of 27 players, the difference was larger, but still a measly 0.3%. If tactics are the answer, it must be on the return of serve, not the serve itself.

This is where the trail runs cold. Return tactics are tougher to quantify than serving strategy, and there’s a limit to how much we can do with the available data. We can tally return winners and induced forced errors (IFEs), points in which the returner ended things with a strong reply. If returners allowed more aces, it should be because they took a more aggressive approach, trading fewer opportunities for better odds of winning when they did make contact. Instead, the record shows that return winners and IFEs fell a whopping 7% from last year to this year. That number supports the theory of a slower surface, and it meets expectations for those players who adopted very conservative return positions, such as Rafael Nadal, whose return winner/IFE rate went down by 3%, and Thiem, whose rate decreased by 7%. But a slower surface and a lower return winner/IFE rate should add up to fewer aces, not more.

Compared to where we started, we have a lot more data but not many more answers. Some signs point to a faster surface, others to a slower; some indicate more aggressive tactics, others more conservative ones. regardless of what we know about the physical makeup of the courts, there are many factors that influence what we refer to as “surface speed.” The hot, humid conditions in Flushing this year surely help complicate things–perhaps a study that took into account the heat index for each individual match would shed more light on these questions. We could also be seeing players adapt to the conditions–whether the heat or the slower surface–in different ways. Everyone may agree about how the courts played this year, but it’s much more difficult to pin down exactly what that means.

Economist: A fit Novak Djokovic could dominate tennis’s future

At The Economist’s Game Theory blog, I wrote about Novak Djokovic’s return to the top:

But Mr Djokovic is playing better in his 32nd year than Mr Federer did, and his more rounded game means that he can compete on all surfaces—even with Mr Nadal on clay—in a way that Mr Federer could not.  The odds are against the Serb reaching 20 majors, but another two or three seasons at the top could easily give him a final total of 17 or 18—enough to move Mr Djokovic out of his default position in third place. Fans of Roger and Rafa have long dominated the debate about who is the greatest male player of all time. But by the end of the decade, Mr Djokovic’s trophy cabinet could well be as bulging as those of his legendary rivals.

Read the whole thing.

Eight Slams, Eight Women’s Champions. How About Nine?

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Italian translation at settesei.it

Buried under the din of the Serena-Ramos story is a remarkable fact about parity in women’s tennis right now. Naomi Osaka was the eighth different grand slam champion in eight events, a streak dating back to Serena Williams’s victory at last year’s Australian Open. Since then, it’s been a different face with every trophy: Jelena Ostapenko, Garbine Muguruza, Sloane Stephens, Caroline Wozniacki, Simona Halep, Angelique Kerber, and Osaka. In the same time span, only three different men have won majors.

The women’s field is so deep that the streak could easily keep going. I built a possible Australian Open draw using the current top 128 players in the WTA rankings, then ran a forecast of the tournament based on each player’s current Elo rating. Here are the title chances for each of the last eight slam winners:

Player              Seed  Title Odds  
Simona Halep           1       16.7%  
Caroline Wozniacki     2        7.1%  
Angelique Kerber       3        5.7%  
Serena Williams       16        5.5%  
Naomi Osaka            7        4.9%  
Sloane Stephens        9        2.6%  
Garbine Muguruza      14        1.8%  
Jelena Ostapenko      10        0.5%  
TOTAL                          44.9%

Altogether, they add up to less than 50%! Put another way, there are better than even odds that we get a ninth different woman giving a victory speech in Melbourne. Here are the players with the best chances:

Player              Seed  Title Odds  
Elina Svitolina        6        8.8%  
Aryna Sabalenka       20        6.6%  
Petra Kvitova          5        5.9%  
Karolina Pliskova      8        3.7%  
Ashleigh Barty        17        3.5%  
Caroline Garcia        4        3.3%  
Madison Keys          18        2.6%  
Venus Williams        21        2.6%  
Mihaela Buzarnescu    23        2.3%  
Julia Goerges         11        2.2%

Ok, yes, Mihaela Buzarnescu seems a little out of place here. But of the other nine players, would any of them represent more of a surprise than Ostapenko, Stephens, or Osaka? By the numbers, three of the top five favorites for the Australian Open haven’t won a major in the last two years.

Given the sheer number of plausible contenders, it’s easy to imagine not just nine different slam winners in a row, but twelve, extending through the entire 2019 season. Consider the possibilities:

This is all rather fanciful, I know. But it’s barely even accurate to say there is a “favorite” when only one woman has a double-digit chance of winning the next major, and her odds are a mere one in six. No single player is likely to win any given grand slam, and only Halep has better than a fifty-fifty shot at winning one over the course of the year.

The chances that the streak extends to twelve are small, but not as low as, say, Osaka’s probability of winning the US Open before the tournament began. We’ve seen that the odds of a ninth different winner triumphing in Australia are about 55%. If that person wins, she’ll probably have earned a rosy forecast for Paris, so the probability of a new winner at the French is lower. And so on, after a tenth or eleventh different champion. If we lower the “new-winner” odds by seven percentage points for each slam, the chances of twelve-slam streak are 3.7%, the same as Pliskova’s probability of becoming number nine. Stranger things have happened. In women’s tennis, the unpredictable has become the norm.

Podcast Episode 32: US Open Recap

Episode 32 of the Tennis Abstract Podcast, with Carl Bialik of the Thirty Love podcast, scrupulously skips the Serena-Ramos controversy and goes straight for the tennis. We look at the resurgence of Novak Djokovic and his US Open final victory over Juan Martin del Potro, consider what the future holds for women’s champion Naomi Osaka and how it compares to a few other rising WTA stars, and outline some difficult choices on the horizon for doubles prodigy Jack Sock.

Thanks for listening!

(Note: this week’s episode is about 60 minutes long; in some browsers the audio player may display a different length. Sorry about that!)

Click to listen, subscribe on iTunes, or use our feed to get updates on your favorite podcast software.

Gender Differences in Point Penalties

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Italian translation at settesei.it

The officiating in Saturday night’s US Open women’s final has become a hot-button issue, to put it mildly. Many of the complaints about Serena Williams’s treatment at the hands of chair umpire Carlos Ramos come down to a belief that Ramos’s actions were sexist. Most of us have seen players–both men and women–act in ways that seem more objectionable than anything Serena did, and anybody paying attention has seen innumerable coaching violations go unpenalized.

There are a few things we can all agree on. First: Not all umpires are the same. Ramos is more strict than, say, Mohamed Lahyani. Second: Officials have a lot of latitude, so something that triggers a penalty in one match may not have the same result in another match. And third: Umpires usually do everything they can not to call game penalties. A lot of matches have at least one warning, whether for coaching, ball abuse, or a variety of other things, but only a small percentage of them escalate to the loss of a point or game. Of course, players typically proceed with caution as well. Once a warning has been called, you don’t see nearly as many rackets smashed or balls sent sailing out of the stadium.

The differences between umpires, and the latitude granted to them within the rules, makes it easy to point to any given call and accuse the umpire of sexism, racism, favoritism, homerism, Fed-hating, Rafa-hating, or good old-fashioned stupidity. The rarity of point and game penalties makes Saturday night’s decisions all the more glaring, since within each umpire’s range of options, they rarely go nuclear and dock an entire game.

Some numbers

Point penalties–let alone game penalties–are so rare that it’s impossible to draw concrete conclusions. Still, let’s take a look at what we have. As far as I know, none of the ATP, WTA, ITF, or USTA have released any data on penalties, the players who receive them, or the umpires who levy them. (This would be a great time to do so, but I’m not holding my breath.) As an alternative, we can turn to the increasingly sizable dataset of the Match Charting Project (MCP), which now spans over 3,500 matches from the 2010s alone.

MCP data is not random, since matches are chosen by charters in part because of their personal interests. But in a way, that’s good for today’s purposes: MCP matches skew in the direction of notability, with a disproportionate number of finals and substantial data for top players, including over 100 matches for Serena. With those caveats in mind, let’s take a look at penalties in matches from 2010 to the present, not including Saturday’s final. The final column, “P%”, is the percent of matches in which a penalty was levied.

Category        Matches  Penalties     P%  
Women (all)        1895         13  0.69%  
Women (slams)       490          6  1.22%  
Women (finals)      228          2  0.88%
  
Men (all)          1689         16  0.95%  
Men (slams)         234          6  2.56%  
Men (finals)        371          5  1.35%

Men receive more point penalties than women in three separate comparisons: All MCP matches, matches at grand slams*, and finals. The grand slam numbers are particularly pertinent because it is the only category in which the umpires are drawn from the same pool. At other events, the ATP and WTA use separate groups of officials.

(I’m ignoring full-game penalties because there’s almost no data. In these 3,500-plus matches, there was only one instance where things escalated beyond the point penalty stage: Grigor Dimitrov’s meltdown at the 2016 Istanbul final.)

* Update: A number of people have pointed out that the grand slam comparison isn’t exactly apples-to-apples, because men play best-of-five. True. I’m not sure, however, if we should expect proportionally more penalties in longer matches. Coaching, for instance, would continue throughout a match until identified as a code violation, and then (one would hope) stop. That said, it is certainly true that on a per-point or per-set basis, the gender gap at majors is smaller than these numbers suggest, though it still leaves us with more point penalties against men.

These numbers aren’t proof of gender fairness, nor do they establish sexism against either women or men. Aside from the limited number of penalties, we know nothing about the actions that led to them, or about similar instances that didn’t trigger penalties. Perhaps men are generally more abusive to officials, so they should receive half again as many–or even more–penalties than women. I don’t know, and it’s likely that nobody else commenting on the Serena-Ramos incident knows either. Anecdotes are a key ingredient in this sort of vitriol. To firmly settle the issue, we’d need to set up a controlled study, perhaps by instructing a set of male and female players to berate umpires in identical ways and then comparing the results. As entertaining as that would be, it’s not going to happen.

None of this is to say that accusations of sexism require statistical support to be valid. They don’t. But in cases where the data is available, especially when it is possessed by some of the very organizations making accusations, it’s a shame that the numbers get ignored. The limited information available to us via the MCP indicates that men are more frequently penalized by chair umpires than women are. The USTA, ITF, and WTA could go a long way to clear up the issue–whether officials are consistently equitable or there is a pattern of harsher treatment of female players–by releasing details of all matches, including the number and causes of warnings and penalties, as well as the identity of the umpires. Alas, the more likely outcome is a few more weeks of unsubstantiated grandstanding.

Economist: An overzealous chair umpire overshadows Naomi Osaka’s impressive victory

I wrote something for the Economist Game Theory blog on the controversy in the US Open women’s final. Here’s one part I hope people remember:

The tennis world will probably be debating Mr Ramos’s calls until the next major rolls around in January. But one thing should not be in doubt: Ms Osaka didn’t need his help to earn her first grand slam title. Excluding the five penalty-determined points, she won 60 of the 110 points played, good for 64% on her own service and 45% on return. A ratio of that quality almost guarantees victory. In addition, all five of the points Ms Williams was docked would have been played on Ms Osaka’s serve. Given the level that the 20-year-old sustained, the first point penalty increased her chances of winning by less than half a percentage point, from 97.8% to 98.2%. Even if Ms Williams had been able to raise her level to equal her opponent’s, the impact would have been less than two percentage points. The game penalty was worth barely a full percentage point, boosting Ms Osaka’s probability of victory from 98.1% to 99.2%. By the time the New York crowd started booing, the match was virtually in the bag.

Read the whole thing.

The Right Amount of Serve-and-Volley

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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.

Juan Martin del Potro’s Daunting Semi-final Assignments

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Italian translation at settesei.it

This afternoon, Juan Martin del Potro will take on Rafael Nadal for a place in the 2018 US Open championship match. Forgive me if this sounds familiar: It’s the third time Delpo and Rafa have squared off in Flushing’s final four. Every time the Argentine has made it this far in New York, it’s been the King of Clay waiting on the other side of the net.

Del Potro could be forgiven for wondering if he was born in the wrong era. Today is his sixth major semi-final, and his fourth against Rafa. The other two weren’t cakewalks either. His first appearance in the last four of a grand slam was at the 2009 French Open against Roger Federer, and his best-ever performance at Wimbledon gave him a semi-final meeting with Novak Djokovic. The only slight positive in all this is that he faced Federer in Paris and Nadal so often in New York. Technically, it could have been worse.

Simply reaching six major semi-finals is an achievement in itself. Since 1977, there have been only 35 players to reach five or more. For each of those players, I calculated the average surface-specific Elo of their opponents, as well as their average chances of winning. Measured by opponent Elo, Delpo has had the fourth most difficult semi-final assignments of any of these players. The table below shows each player’s number of semi-finals, number of wins, average chance of winning those matches (“Avg p(W)”) and the Elo rating of their average opponent (“Avg Opp Elo”):

Player                 SFs  Wins  Avg p(W)  Avg Opp Elo  
David Ferrer             6     1       35%         2202  
Pat Cash                 5     3       22%         2194  
Stan Wawrinka            9     4       35%         2163  
Juan Martin del Potro    6     ?       35%         2161  
Vitas Gerulaitis         7     2       36%         2146  
Mats Wilander           14    11       48%         2122  
Jo Wilfried Tsonga       6     1       31%         2122  
Michael Chang            8     4       46%         2121  
Novak Djokovic          31    22       62%         2115  
Andy Murray             21    11       52%         2114

Like Delpo, many of these guys had one frequent foe. David Ferrer drew Djokovic in three semis. Pat Cash faced Ivan Lendl three times in his five chances. Vitas Gerulaitis kept earning meetings with Bjorn Borg. Stan Wawrinka hasn’t played more than two semis against any particular opponent, but that doesn’t mean his draws have been any easier: He’s faced Djokovic, Federer, and Andy Murray twice each.

Djokovic and Murray pop up at the bottom of the top ten largely because of Federer and Nadal. It’s a tough era, even if you hold a Big Four membership card. Roger and Rafa have had it easier, ranked 24th and 26th in opponent Elo*, in part due to the number of majors they contested before Djokovic and Murray had fully developed–and because they generally avoided playing each other.

* Federer’s average opponent has had an Elo of 2056, and Nadal’s has had a 2045 Elo. Michael Stich is the only player on this list whose opponents’ Elos averaged below 2000.

Today’s match gives Delpo an opportunity to put himself a bit closer to Wawrinka’s category and surpass the likes of Ferrer and Jo Wilfried Tsonga, who reached only one major final each. Based on his own Elo and those of his opponents, del Potro has had about a one-in-three chance of winning his semis. The 2018 US Open represents his sixth, meaning we’d expect two final appearances thus far. Then again, it’s one thing to run the numbers; it’s another thing to beat Rafael Nadal in a major semi-final … twice.