Italian translation at settesei.it
Of the general ways in which points end–winners, unforced errors, and forced errors, which is the most common? It’s so basic a question that I’d never thought to investigate it. As it turns out, other people have, and they’re making tenuous claims based on their results.
A friend sent me a link to this advertisement for an instructional course, which–eventually, far into a painfully slow video–explains that more points on the pro tour end in forced errors than in winners or unforced errors. And because of this, the video argues, you can use some of the same patterns the pros use with the goal of generating forced errors. Apparently, aiming for winners is too risky, as is waiting for unforced errors.
Pedagogically, it seems reasonable enough to encourage patience and tactical conservatism. I don’t know the first thing about helping amateurs improve their tennis game, and I’ll happily defer to the experts.
However, the use of pro tennis data sparked my interest. I was immediately skeptical of these claims, which were apparently based on Grand Slam matches from 2012.
Using my datasets extracted from IBM Pointstream’s records of the last several slams, I tested the 2015 French Open and the 2015 US Open, tallying winners, unforced errors, and forced errors for men and women at both events. Here’s how they break down:
Dataset Winners Unforced Forced
FO Men 33.8% 32.9% 33.3%
FO Women 32.7% 37.8% 29.5%
USO Men 34.3% 31.6% 34.1%
USO Women 31.0% 38.0% 30.9%
On both surfaces, men’s points split fairly evenly among the three categories. For women, winners are roughly even with forced errors (though there are more winners on clay) and unforced errors are the most common type of point-ending shot.
The Pointstream-based dataset has limitations, though, and you might have already guessed what it is. A sizable percentage of forced errors are serve returns, which don’t really seem pertinent to a discussion of tactics. We can separate aces from winners and double faults from unforced errors, but not forced error returns from forced errors.
For that, we need the resources of the Match Charting Project. That data gives us almost 1500 matches (evenly split between men and women) once we limit our view to tour-level contests. The MCP dataset contains everything Pointstream does–winners, unforced and forced errors–and much, much more. For our purposes, the key addition is rally length, which allows to differentiate between forced error returns and forced errors that came later in rallies.
With the MCP data, we can remove serve statistics from this discussion altogether, excluding aces, double faults, and forced error returns, none of which are tactics in the sense we usually use the word.
Here’s the frequency of each type of point-ender:
Dataset Winners Unforced Forced Men 32.5% 45.8% 21.7% Women 32.4% 49.4% 18.2%
When serves are no longer cluttering the picture, winners retain their relative importance, but the distribution of errors changes enormously. Now, we see that once the returner gets the ball back in play (or receives a serve he or she should be able to put back in play), unforced errors outnumber forced errors by more than two to one.
(I also calculated clay-specific numbers, and all the rates were within one percentage point of the overall averages.)
Forced errors are the most common type of point-ender in only 14 of 728 charted men’s matches and 4 of 751 charted women’s matches. Even if you’re concerned about the representativeness of the MCP sample or the error-labeling tendencies of the charters and add make substantial adjustments to allow for them, these results overwhelming establish that unforced errors are the most common way in which rallies end.
I’m not sure how applicable the tactics and tendencies of pro players are to amateur coaching, so it’s possible that these numbers are irrelevant to a great deal of coaching pedagogy. But if you’re going to base your instructional technique on pro tennis stats, it seems reasonable to start by getting the numbers right.
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