Perhaps the most unquestioned piece of conventional wisdom in tennis is this: after breaking serve, a player is particularly vulnerable to being broken himself. It certainly seems to be true–to take just one example, in the Isner/Karlovic match last week, there were only two breaks of serve, and they were consecutive.
As with most bits of conventional wisdom, it’s not clear exactly what people mean by it. When Djokovic crushes someone 6-0 6-1, do we really think his serve is more vulnerable after each of his five or six breaks than it is after the one game his opponent holds? When a player does break back, is he then more vulnerable in his next service game?
Today, I’ll try to address the more basic versions of the cliche. The results are a bit surprising.
I’m working with all of the 2011 Australian Open matches from courts where Hawkeye was in place. That’s about 80 of the men’s singles matches, and roughly the same number of women’s matches. I’ve run the numbers on both genders but will keep them separate, for reasons that will become clear.
These matches give us over 2,700 men’s games across about 300 sets, and nearly 2,000 women’s games over a bit more than 200 sets.
Breaking back: Men
At this year’s Aussie Open, 24% of all men’s games were service breaks. If we take the conventional wisdom literally, we would hypothesize that in the game following a service break, another break would occur more than 24% of the time.
But it doesn’t. In the game following a service break, the server is broken only 19.5% of the time. (I’m excluding service breaks that end a set or take a set to a tiebreak.) In other words, in the aggregate, a player is more likely to hold serve after breaking serve than he is after his opponent holds.
Of course, as I suggested by mentioning Djokovic a moment ago, there’s a huge selection bias here. A player who breaks serve is (all else equal) likely to be a better player than one who doesn’t. The best players in the most lopsided matches are breaking serve frequently, and because they are the better player, it makes sense that they are more likely (again, all else equal) to hold their own serve.
Without looking at individual matchups, it’s not immediately clear how to address this problem. For one thing, I’m not convinced it’s a problem. When Federer broke Kohlschreiber today, a commentator may have said, “Roger is particularly vulnerable here, let’s see if he can consolidate the break.” One could easily respond: “Roger just showed us he’s in tremendous form; the very fact he just broke serve is an indication that he’s less vulnerable than usual on serve right now.” And so it proved: Roger broke four times; Kohlschreiber never broke back.
What might be more instructive is to look at situations where the player who broke serve is considered to be roughly equal or inferior to his opponent. Had Kohlschreiber broken serve early in the match, even given the assumption that he must be playing well in order to do so, the conventional wisdom would suggest that Federer is more likely to break back. Perhaps that’s true. It’s not something I can answer today–quantifying the matchups is beyond the scope of this afternoon project. It’s also problematic in that it would also shrink the size of our already-small dataset.
In any event, it is clear that we can’t take this bit of conventional wisdom at face value. It may be true in certain scenarios–some players may crumple under the pressure of consolidating a break, and others may rise to the occasion after losing serve. But it is wrong to say that, in general, players are more vulnerable on serve after a break.
Breaking back: Women
As you might expect, breaks of serve are more prevalent in the women’s game, as are breaks-following-breaks.
At the 2011 AO, women broke serve 36.5% of the time. In games following breaks of serve, they broke 36.0%. In contrast to the men’s results, this suggests that in the women’s game, a service break doesn’t tell us as much about the strength of the player who has accomplished the break–or, if it does, that a server is more vulnerable after breaking serve. Anecdotally, it certainly seems that differences in mental strength play a larger role in WTA matches, so I would expect that the break-back rate would be higher.
As I’ve said, this is far from the final word. As usual, the conventional wisdom masks many subtleties that only further analysis can unearth.