The Luck of the Tiebreak

Italian translation at settesei.it

Yesterday, I introduced a method to separate “good tiebreak playing” from “good tennis playing.”  For the most part, better players win more tiebreaks, but some guys win more tiebreaks than their general betterness would suggest.

That impels some questions: Why do those players win more tiebreaks than expected?  Do they do so regularly?  Is it their style of play?  Is it magical tiebreak-fu?  Is it possible to get through two paragraphs of a post about tiebreaks without mentioning John Isner?

Here are two hypotheses, which I will discuss in turn:

  1. Players who win more tiebreaks than expected do so because their game is suited to tiebreaks–which probably means that they serve particularly well.
  2. Player who win more tiebreaks than expected do so because, in some intangible way, they are very good at tiebreaks, perhaps due to clutch play, calm under pressure, or intimidation of their opponents.

The server advantage hypothesis

Earlier this week, I reported my results that players seem to serve worse (fewer aces, fewer points won) in tiebreaks than in the sets that preceded those tiebreaks.  If everyone declined the same amount, everyone would win roughly the number of tiebreaks we expect of them.

But much more likely, some players do not see their serves decline in tiebreaks.  Some might even improve in breakers.  If they do, they outperform the average, and they win more tiebreaks than expected.

Another angle here is that for some players, a bit of serve decline doesn’t matter much.  In last week’s match between Isner and Kevin Anderson, Isner won 79% of service points and Anderson won 77%.  Nearly one in five serves for the entire match went for aces–imagine how many more were service winners.  If both players served a bit more conservatively in the breakers, would we even notice?  When Fernando Verdasco starts playing it safe, it’s impossible not to notice–and easier to beat him in a breaker.  Perhaps that isn’t so for the likes of Isner.

These are appealing theories.  (Especially to me–I thought them up myself and believed in them for several hours.)  However, the numbers don’t bear them out.  There is no consistent statistical relationship between big serving and outperforming tiebreak expectations.  To take a few examples: Isner is a tiebreak monster–probably the best tiebreak-player of this generation.  Pete Sampras and Roger Federer are also among the greats.  Below average, though, are the likes of Ivo Karlovic, Sam Querrey, Marc Rosset, and Robin Soderling.

Let’s try another…

The intangibles hypothesis

If there is some intangible mental factor that causes some players to win more tiebreaks than they would otherwise, it’s impossible to test for that effect directly–if it were possible, it wouldn’t be intangible.

But, if some players had that tiebreak-fu, they would probably hold on to it for more than a single season.  For instance, when Novak Djokovic won an impressive 19% and 16% more tiebreaks than expected in 2006 and 2007, respectively, we should have been able to assume that he’s really good at tiebreaks, then predict that he would continue to excel in breakers in 2008.  Yet in 2008, 2009, and 2010, Djokovic barely outperformed average, winning 2% or 3% more than expected.  Ok, so we have a new forecast for Novak in the new decade: just a bit more tiebreak-magic than others.  Yet in 2011, Djokovic won 10% fewer tiebreaks than expected.  He’s 9% below average this year.

Sometimes, these changes might be explained by confidence.  But more often, they are just plain random.  While a few players (including Isner and Federer) put up great numbers every year, the vast majority of the field fluctuates, seemingly at random.  The year-to-year correlation for the population of players with at least 15 tiebreaks in two consecutive years (going back to 1991) is almost exactly zero.  (Set the bar higher if you wish; still barely distinguishable from zero.)

If tiebreak-related intangibles were widespread, there would be some kind of year-to-year correlation.  Perhaps a small number of players do have that magic, but for the purposes of most analysis, it is more accurate to assume that when it comes to a player’s overperformance in tiebreaks, his record one year has very little to do with how he’ll perform the next.

One tiny ray of light

This gets a bit frustrating after a while.  It seems that something should turn up as the cause of tiebreak excellence.  One simple stat does, to a small degree: number of tiebreaks played.  In other words, the guys who play the most tiebreaks tend to be the ones who beat expectations in those tiebreaks.

The connection that immediately springs to mind (after serving prowess, which we’ve already discarded) is practice.  The more match-court breakers you play, the better you become.  Isner, Federer, Sampras–they spend more time at 6-6 than almost anyone, and their tiebreak records are among the best.

Of course, the causation could go the other way.  Perhaps confidence in one’s tiebreak skills cause a player to be more comfortable going to a breaker.  While Djokovic or Andy Murray would press particularly hard for a break a game away from a 6-4 or 7-5 set, Isner is comfortable cruising into a tiebreak.

It’s a minor effect (r < 0.2), one that doesn’t explain anywhere near the observed year-to-year variance in tiebreak under- and over-performance.  But it’s something.

The implications of the luck of the tiebreak

What if overperforming or underperforming your expected tiebreak performance is, essentially, luck?  Or more generally (and safely) speaking, what if it says little about you likelihood of being good or bad at tiebreaks in the future?

For one thing, it would have a major impact on forecasting.  If tiebreak performance one year doesn’t predict tiebreak performance the next, players with extreme under- or over-performances one year can be expected to regress to the mean the following year.  It’s unclear exactly what that would mean in practice, but if you take away Feliciano Lopez‘s five tiebreaks more than expected in 2011, you’re left with a player who probably isn’t ranked within the top 20.  You would expect a decline as he stops winning quite so many breakers.

On a more practical level, these implications might aid the confidence of players with middling tiebreak records.  If you’re Andreas Seppi, who has a career losing record in breakers, you might be excused for some negativity when you reach 6-6 against, say, Karlovic.   But if you know your own poor record is only loosely related to your skills, and Karlovic’s record isn’t nearly as good as it looks, you might take a different approach.  Indeed, Seppi underperformed tiebreak expectations every year from 2006 to 2011, but has won more than expected this season–including one breaker each against Djokovic and Isner.

There’s plenty more work to do here–calling a couple of popular hypotheses into question hardly puts the issue to bed.  But if we’ve learned nothing else this week, it is that tiebreaks are not at all what they seem.  The players you think are masters are often middling performers, and regardless of the conventional wisdom, the breaker is about a whole lot more than a big serve.

Who Actually Excels in Tiebreaks?

Italian translation at settesei.it

I’ve never understood the fixation that some fans and commentators seem to have with tiebreak winning percentage.  Sure, winning tiebreaks is nice, but it seems obvious that the main cause of exemplary tiebreak performance is being good at tennis.  Though some players may in fact be better than others at this facet of the game, a big part of what tiebreak winning percentage tells us is about general tennis skill.

In other words, Roger Federer is very good at tiebreaks because he is very good at serving and returning, the same skills that get him so many wins, regardless of whether any of the sets go to tiebreaks.

If we ignore tiebreak winning percentage, what are we left with?  It’s still tempting to wonder whether some players have a kind of special skill–calm under pressure, a particularly consistent serve–that leads them to outperform expectations in breakers.

The key word there is “expectations.”  Given Federer’s general ability on the tennis court, we should expect him to win most tiebreaks–for example, two of the last three breakers he’s played came against Stanislas Wawrinka, who he should beat regardless of the format.  But our intuition will fail us if we look at Federer’s match record and try to estimate how many tiebreaks he should have won, then compare the “should” to the “did.”

Expected tiebreaks

Sounds like something computers do better than humans.  Given a player’s percentage of service and return points won in a certain match, we can estimate how likely he was to win a tiebreak–on the assumption that his performance level stayed the same throughout the match.

If two players are equally matched, each one would be “expected” to win 0.5 tiebreaks.  That’s nonsensical for a single match, but over the course of this season, we see that of John Isner‘s 53 tiebreaks, the algorithm would expect him to win 29.  In fact, he has won 38, exceeding expectations (in raw terms, anyway) more than anyone else on tour this year.

This gives us two stats that offer more insight into a player’s tiebreak performance than “tiebreaks won” and “tiebreak winning percentage.”  The raw number, the difference between actual tiebreaks won and expected tiebreaks won, tells us how many additional sets a player has taken because of his tiebreak performance.  Call it TBOE: TieBreaks Over Expectations.  A similar rate stat is derived by dividing TBOE by the number of tiebreaks, allowing us to compare players regardless of how many tiebreaks they played.  Call that one TBOR: TieBreak Outperformance Rate.

As we’ve seen, Isner is the 2012 king of TBOE, performing well in tiebreaks and playing far more of them than anyone else on tour.  Yet three players–Steve Darcis, Andy Murray, and Jurgen Melzer–have done better by TBOR, exceeding expectations at a greater rate than Isner has.  Darcis is particularly remarkable, winning 16 of his 19 tiebreaks through last week, despite his serve and return rates in those matches suggesting he should have won only 10 of them.

(And in Vienna on Monday, he won another one, extending his already untouchable lead over the pack.)

I’ll have more to say about this tomorrow, including a look at just how much meaning we can extract from TBOE and TBOR.  In the meantime,  look after the jump for the current 2012 leaderboard–through Shanghai, sorted by TBOR, minimum 15 tiebreaks.

Continue reading Who Actually Excels in Tiebreaks?

What Matters in Tiebreaks?

Italian translation at settesei.it

Players and fans tend to look at tiebreaks as a unique part of the sport of tennis, perhaps one susceptible to special skills.  The ATP website last week devoted an article to what those skills might be.  Players generally seemed to agree that it was nice to have a good serve, and a good return would also be handy.  Clearly, more analysis is needed.

Let me give you my hypothesis.  Tiebreaks are pressure packed, and pressure can affect any part of a player’s game.  But in general, they should impact some parts more than others.  You could make the case for either side of the ball–on the one hand, serving is a more “automatic” activity; on the other, there’s more time to think before each serve, and thinking can be dangerous when the pressure is on.  This is where it’s nice to have some data.

I found 388 tiebreaks from the last eight ATP slams.  For each one, I compared each player’s winning percentage on serve during the first 12 games of the set to his winning percentage on serve during the tiebreak.  If players were robots, there might be a difference between the set and the tiebreak for any given match, but in general, the numbers should be the same.

But players aren’t robots.  As it turns out, players win more return points than expected during tiebreaks.  The difference is noticeable if not enormous: about one more return point than expected every three matches.

Thus, tiebreaks are different from the sets that precede them in one of two ways.  Either some players are unable to serve up to their usual standard during tiebreaks, or some players manage to raise their return game in tiebreaks.

A breakdown by tournament suggests the answer.  The difference between server winning percentage in sets and tiebreaks is about the same for the Australian Open, the US Open, and Wimbledon, but is less than half as much at the French.  It seems, then, that faster courts give returners a bigger boost in the breaker.  A more likely interpretation is that servers are unable to hold on to their advantage on faster courts.  There’s less of an advantage to lose on clay.

My hypothesis at the outset focused on pressure, and combined with the numbers, it suggests that players are more affected by pressure when serving than when returning.  It’s also possible that players find it more difficult to get into a serving rhythm with only two serve points at a time.  It’s also possible that returners are less likely to concede aces during tiebreaks, meaning that the same serve quality and return potential results in more return points won.

Whether it is a matter of server timidity or returner aggression, there are certainly fewer aces in tiebreaks.  In these 388 tiebreaks, there were 83 fewer aces than would be expected if players kept acing at the rate of their first twelve games.  Given the relative infrequency of aces, that’s a more striking decrease than that of service winning percentage in general.

This analysis is hardly the final word.  But for aspiring tiebreak masters, it does offer a slightly more specific prescription than “get better at tennis.”  Rather than assuming that the tiebreak is all about the serve, recognize that returners have a slight advantage.  On serve, players can improve simply by ignoring the pressure (easy, right?) and serving as well as they did during the set.  When returning, players can be more aggressive in the knowledge that in general, servers will not be.

After all, a good serve may be the key to tiebreak success, but only if the serve is as good as usual in the breaker.