Cool Down Tennis

This is a guest post by Carl Bialik.

Imagine you’re named boss of tennis. Right after being sworn in by Rod Laver and Martina Navratilova, you’re handed an empty wall calendar. You make the schedule for 2018. What’s your first move?

Mine would be to move Indian Wells and Miami earlier in the calendar, and the Australian Open later, after the two U.S. Masters tournaments.

I never wanted this more than while sweating my way around the Indian Wells grounds in search of shade last month. I wasn’t alone. The only full sections of the main stadium during day sessions were the ones protected from the sun. Around the fan-friendly venue, there are plenty of seats in the shade — under tents, or in Adirondack chairs that shade-seeking people push ever closer to the screen as the sun shifts. The players can only wait for shade to slowly descend on the court. Jack Sock needed a towel holding 50 ice cubes to cool down.

Sweating in the grass

 

Sure, it was unusually hot at this year’s Indian Wells tournament. But the climatological averages are clear: It’s hot in the California desert and in the Florida sunshine in March, and in the antipodean summer in January. It’d be cooler in Indian Wells, Miami and Melbourne if the two Masters events moved two months earlier and led up to the year’s first Grand Slam in March. Each of the two-week events would be, on average, 4 to 10 degrees Fahrenheit cooler each year. (The precipitation would be about the same, so Miami men’s finalist Rafael Nadal might continue to bemoan humidity, request sawdust and show more than he’d planned beneath his shorts; while women’s champ Johanna Konta might keep having to change clothes midmatch because they’ve accumulated approximately five kilograms of sweat.)

I’m using the averages because I don’t want to make too much of an unseasonably hot Indian Wells, or too little of an unusually cold March in Miami. But the averages might understate the problem because it’s precisely the outliers we’re worried about. A nudge downward of a few degrees, on average, could translate into a big drop in the probability of an unbearably hot fortnight — say, from 25 percent to 5 percent.

Changing the tennis calendar would also mean less daylight. That wouldn’t be so good for the nickname Sunshine Double, but it’d be good for tennis. Until more tennis stadiums adopt overhanging partial roofs — but for sun, not for rain — shorter days means less sun for fans to contend with and more reason to fill the seats. Plus, night tennis is exciting. The venues already have plenty of lights and evening sessions.

Scrambling the schedule would do more than cool down tennis. The three midyear majors’ proximity to each other helps the sport carry some momentum and mainstream buzz from one to the next. The Australian Open squanders all that in the four-month gap between its end and the start of the French Open. There’s even a month between the Aussie Open and the next big event.

The other three majors also get opening acts, to help players build up familiarity with the surface and for fans to build anticipation. The Australian Open gets two weeks at the start of the season — without so much as a 500 event on the men’s side.

The lack of buffer between the offseason and Melbourne also means it loses some players still recovering from the end of the previous season. That was the case this year with Juan Martin del Potro, who skipped this year’s first major after winning the Davis Cup with Argentina in November.

Imagine instead starting the season with Indian Wells and Miami — or Miami, then Indian Wells, while we’re scrambling things, for the convenience of travel from the sport’s power center of Europe — using the same courts and balls as Melbourne. Follow that month — or less, if one or both of the U.S. early-year Masters succumbs to the reality that they could be just a week — by Doha and Dubai, then Brisbane, Sydney and the like, before the main event in Melbourne at the start of March. We’d start the season with a real hard-court swing, ending with the first major.

From Australia, the tour could stay in the southern hemisphere. The swing through South America has a long history and a terrible spot on the current calendar. It was traditionally played on clay but some of its biggest events are moving to hard courts — first (North American) Acapulco, now, maybe, Rio, in search of Masters status — to the chagrin of Nadal and others. Too many players simply don’t think it’s worth it to compete on clay for a few weeks if that’s followed by a month of hard-court events. But move Indian Wells and Miami, and South American clay could move a month later in the calendar — while slightly tempering what Nadal bemoans as “too extreme” weather conditions by an average of 1 degree. The swing would give way seamlessly to Houston, Charleston and the European clay spell — which, by the way, would absorb Bucharest, Hamburg, Umag, Bastad and Gstaad from their awkward post-Wimbledon calendar slots. And no one would suggest Miami move to green clay.

We’d be left with a coherent calendar with five seasons of roughly equal length and importance, four with a major and one with the year-end finals: (1) Outdoor hard courts in the U.S., the Middle East and Oceania, followed by (2) clay in the Americas and Europe, (3) English and German grass (with Newport for those who want to visit the sport’s hall of fame), (4) North American and Asian outdoor hard courts, and (5) European indoor hard courts (absorbing the current winter events such as St. Petersburg and Rotterdam) culminating in wherever the tours’ multiplying year-end finals are calling home that year. And let’s play Davis Cup and Fed Cup at the same time — the tours acting in sync; what a concept! — on weekends at the edge of the five new seasons, giving hosts a wider range of sensible surfaces to choose from, and creating the option for combined venues if men and women from the same country are hosting the same round. (Prague in 2012 would’ve been tennis nirvana.) Or, hell, consider merging the events.

Could all this happen? Sure — if tennis power were centralized in a person or people who prioritize the overall good of the global game. Without a radical transformation of tennis, though, it’ll be slow going: It took years for the idea of lengthening the grass-court season by a week to become reality.

Carl Bialik has written about tennis for fivethirtyeight.com and The Wall Street Journal. He lives and plays tennis in New York City and has a Tennis Abstract page.

The Five Big Questions in Tennis Analytics

Italian translation at settesei.it

The fledgling field of tennis analytics can seem rather chaotic, with scores of mini-studies that don’t fit together in any obvious way. Some seem important but unfinished while others are entertaining but trivial.

Let me try to impose some structure on this project by classifying research topics into what I’ll call the Five Big Questions, each of which is really just an umbrella for hundreds more (like these). As we’ll see, there are really six categories, not five, which just goes to show: analytics is about more than just counting.

1. What’s the long-term forecast?

Beyond the realm of the next few tournaments, what does the evidence tell us about the future? This question encompasses everything from seasons to entire careers. What are the odds that Roger Federer reclaims the No. 1 ranking? How many Grand Slams will Nick Kyrgios win? How soon will Catherine Bellis crack the top ten?

The most important questions in this category are the hardest ones to answer: Given the limited data we have on junior players, what can we predict–and with what level of confidence–about their future? These are questions that national federations would love to answer, but they are far from the only stakeholders. Everyone from sponsors to tournaments to the players’ families themselves have an interest in picking future stars. Further, the better we can answer these questions, the more prepared we can be for the natural follow-ups. What can we (as families, coaches, federations, etc.) do to improve the odds that a player succeeds?

2. Who will win the next match?

The second question is also concerned with forecasting, and it is the subject that has received–by far–the most analytical attention. Not only is it fun and engaging to try to pick winners, there’s an enormous global industry with billions of dollars at stake trying to make more accurate forecasts.

As an analyst, I’m not terribly interested in picking winners for the sake of picking winners. More valuable is the quest to identify all of the factors that influence match outcomes, like the role of fatigue, or a player’s preference for certain conditions, or the specifics of a given matchup. Player rating systems fall into this category, and it’s important to remember they are only a tool for forecasting, not an end to themselves.

As a meta-question in this category, one might ask how accurate a set of forecasts could possibly become. Or, posed differently, how big of a role does chance play in match outcomes?

3. When and why does the i.i.d. model break down?

A lot of sports analysis depends on the assumption that events are “identically and independently distributed”–i.e. factors like streakiness, momentum, and clutch are either nonexistent or impossible to measure. In tennis terms, the i.i.d. model might assume that a player converts break points at the same rate that she wins all ad-court points, or that a player hold serve while serving for the set just as often as he holds serve in general.

The conventional wisdom strongly disagrees, but it is rarely consistent. (“It’s hard to serve for the set” but “this player is particularly good when leading.”) This boils down to yet another set of forecasting questions. We might know that a player wins 65% of service points, but what are her chances of winning this point, given the context?

I suspect that thorough analysis will reveal plenty of small discrepancies between reality and the i.i.d. model, especially at the level of individual players. More than with the first two topics, the limited sample sizes for many specific contexts mean we must always be careful to distinguish actual effects from noise and look for long-term trends.

4. How good is that shot?

As more tennis data becomes available in a variety of formats, the focus of tennis analytics will become more granular. The Match Charting Project offers more than 3,000 matches worth of shot-by-shot logs. Even without the details of each shot–like court position, speed, and spin–we can start measuring the effectiveness of specific players’ shots, such as Federer’s backhand.

With more granular data on every shot, analysts will be able to be even more precise. Eventually we may know the effect of adding five miles per hour to your average forehand speed, or the value of hitting a shot from just inside the baseline instead of just behind. Some academics–notably Stephanie Kovalchik–have begun digging into this sort of data, and the future of this subfield will depend a great deal on whether these datasets ever become available to the public.

5. How effective is that tactic?

Analyzing a single shot has its limits. Aside from the serve, every shot in tennis has a context–and even serves usually form part of the backdrop for other shots. Many of the most basic tactical questions have yet to be quantified, such as the success rate of approaching to the backhand instead of the forehand.

As with the previous topic, the questions about tactics get a lot more interesting–and immensely more complicated–as soon as Hawkeye-type data is available. With enough location, speed, and spin data, we’ll be able to measure the positions from which approach shots are most successful, and the type (and direction) that is most effective from each position. We could quantify the costs and benefits of running around a forehand: How good does the forehand have to be to counteract the weaker court position that results?

We can scrape the surface of this subject with the Match Charting Project, but ultimately, this territory belongs to those with camera tracking data.

6. What is the ideal structure of the sport?

Like I said, there are really just five questions. Forecasting careers, matches, and points, and quantifying shots and tactics encompass, for me, the entire range of “tennis analytics.”

However, there are plenty of tennis-related questions that we might assign to the larger field of “business of sports.” How should prize money be distributed? What is the best way to structure the tour to balance the interests of veterans and newcomers? Are there too many top-level tournaments, or too few? What the hell should we do with Davis Cup, anyway?

Many of these issues are–for now–philosophical questions that boil down to preferences and gut instincts. Controlled experiments will always be difficult if only because of the time frames involved: If we change the Davis Cup format and it loses popularity, is it causation or just correlation? We can’t replicate the experiment. But despite the challenges, these are major questions, and analysts may be able to offer valuable insights.

Now … let’s get to work.

3,000 Matches!

Italian translation at settesei.it

Last week, the Match Charting Project hit an exciting milestone: 3,000 matches!

The MCP has been logging shot-by-shot records of professional matches for about two and a half years now, and in doing so, we’ve built an open dataset unlike anything else in the tennis world. We have detailed records of at least one match from almost every player in the ATP and WTA top 200s, and extensive data on the top players of each tour. Altogether, we’ve tracked 450,000 points and over 1.7 million shots.

The research that could be conducted using this data is almost inexhaustible, and we’ve barely scraped the surface. My work on Federer’s new-and-improved backhand was just one example of what the Match Charting Project has made possible.

One of the most valuable aspects of the project last year was the addition–spearheaded by Edo–of nearly all men’s and women’s Grand Slam finals back to 1980. (We’re still missing a handful of them–if you can help us find video, we’d be very grateful!) This year, we’ve taken on another challenge: All of the head-to-heads of the ATP Big Four. Already, we’ve covered the 37 meetings of Federer and Nadal (through yesterday’s Miami final), and we’re near the 75% mark for the 216 total matches contested among these four all-time-greats.

Meanwhile, we’re continuing to add a broad range of matches almost as soon as they happen, including over 20 each from Indian Wells and Miami,  along with the occasional ITF and Challenger contest. While the data is skewed toward a handful of popular players, we’ve been careful to amass several matches for nearly every player of consequence on both tours.

If you’re interested in tennis analytics, I hope you’ll consider contributing to the project by charting matches. This data doesn’t magically collect itself, and like most volunteer-driven endeavors, a small number of contributors are responsible for a substantial percentage of the work. Even a single match is a useful addition, and the biggest risk you face is that you’ll get hooked.

Click here to find out how to get started.

Here’s to the next 3,000 matches!