Italian translation at settesei.it
Once I started charting matches–carefully watching and notating every shot–I thought I noticed a trend after “let” serves. It seemed that players missed far more first serves than usual after a let, and when players landed a post-let first serve, their offering was weaker than usual.
Now that we have nearly 500 pro matches in the Match Charting Project database, including at least 200 each from both the ATP and the WTA, there’s plenty of data with which to test the hypothesis.
To my surprise, there’s no such trend. If anything, players–men in particular–are more likely to make a first serve after a let cord. When they do, they are at least as likely to win the point as in non-let points, suggesting that the serve is no weaker than usual.
Let’s start with the ATP numbers. In over 1,100 points in the charting database, the server began with a let. He eventually landed a first serve 62.8% of the time, compared to 62.0% of the time on non-let points. When he made the first serve, he won 73.3% of points that began with a let serve, compared to only 70.6% of first-serve points when there was no let.
More first serves in, and more success on first serves. The latter finding, with its difference of 2.7 percentage points, is particularly striking.
Of the trends I had expected to see, only one is borne out by the data. Since a net cord let is only millimeters away from a fault into the net, it seems logical that net faults would be more common immediately after a let than otherwise. That is the case: 15.7% of men’s first serves result in faults into the net, but after a let, that figure jumps to 17.0%.
When we turn to WTA matches with available data, we find that the post-let effect is even stronger. In non-let points, first serves go in at a 62.8% rate. After a first-serve let, players record a 65.3% first-serve percentage. Given that first-serve percentages are usually concentrated in a relatively small range, a difference of 2.5 percentage points is quite significant.
The WTA data tells a different story than the ATP numbers do when we look at the end result of those first serves. On non-let points, WTA players win first-serve points at a 62.8% rate, while after a first-serve let, they win these points at only a 61.8% clip. It may be that some women approach post-let first serves a bit more conservatively, and they pay the price by winning fewer of those points.
WTA players also appear to miss a few more post-let first serves into the net, though the difference is not as striking as it is for men. On non-let points, net faults make up 16.2% of the total, and after first-serve lets, net faults account for 16.7% of first serves. Of all the numbers presented here, this one is most likely to be no more than random noise.
It turns out that let serves don’t have much to tell us about the next serve or its outcome–and that’s not much of a surprise. What I didn’t expect was that, after a let serve, professionals are a bit more likely than usual to find success with their next offering.
If you like watching tennis and think this kind of research is worth reading, please consider lending a hand with the Match Charting Project. There’s no other group effort of its kind, and the more matches in the database, the more valuable the analysis.
You forgot to factor in the uncertainty principle, which says that as observers we affect the outcome. When someone is watching a match & there’s a let first serve and they say to themself, “Bet he misses this next one, or else it’s a softie,” then an additional 2.8 percent of the time that will in fact happen. The problem is, you’re the only one who thinks this & you don’t watch enough matches to impact the overall stats.
It also doesn’t help that I watch most matches on replay!
Interesting results, and surprising to me too – I would have expected the same as you on the ATP side. Did you look at let second serves (smaller sample size I know)? Or let first serves followed by a fault? In the latter case there are often gasps around the stadium, especially on a big point, because some people think the player has double-faulted. I wonder if that added suspense changes the likelihood of a double fault.
You’re right, the second-serve-let sample is tiny. It’s way less than the first-serve sample, so I don’t think the results are worth discussing yet.
These results don’t surprise me. If you hit a hard first serve and “almost” nail it, it’s easier (to me) to repeat that same motion, stretching the swing just a bit to get that millimeter. And with that confidence comes a little more power. Do serves in after a first-serve let have a higher mph than a non-let first serve? I would guess that they do.
Would be great to have serve speed here. However, even the occasional dataset I’ve seen with serve speed doesn’t have serve speed on lets. (I’m not sure speed even shows up on on-court displays on lets.)
As always, an interesting question to look at it with all of this excellent data you are harvesting. In this case, the results seem intuitive to me. When your first serve clips the net, the server gets instant feedback on his/her last delivery. Server now knows next delivery needs to be adjusted by pushing up a little more with the legs, maybe adding spin to play it a little safer.
Here is another question: Where does the next serve go after a first serve let? In other words, if the server goes down the T and hits a let, is he more likely to go T again, or has he played his hand so he now chooses to go out wide? My guess is that he attempts the exact same serve more often than not!
Unfortunately I don’t track the direction of the let. Your hypothesis makes sense, though I wonder: it seems that players often go with a different serve after the let, which would mean the motion isn’t quite as repetitive as if he went for the same serve. (The guessing game the return has to play might explain the higher winning percentage, too.) Also, pros tend to go through their entire pre-serve routine again after a let, which makes me think they are trying to “reset” their brain as if it’s a new point. I would think that would lessen the effect of having just hit a first serve that almost made it.
What if you control for players ability as you did in your previous researches?
That is, checking the expected precentage of the same player by his overall stats at the same match, and then adding up the numbers.
I checked with that approach, and the results are very similar.