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Yesterday we argued that Federer’s unusually strong backhand anchored his Australian Open win over Rafael Nadal, and today we found a startling statistical basis for that claim. It comes courtesy of the always helpful Jeff Sackmann at TennisAbstract. Relative to other sports, tennis remains fairly data-poor, but Sackmann’s hacking away at the problem with his Match Charting Project, which rallies volunteers to log tennis matches shot-by-shot, producing a granular picture of a sport usually painted in simplistic narrative strokes.

Sackmann used those logs to home-brew a stat he calls backhand potency (BHP), meant to gauge the efficacy of that particular stroke over the course of a match by assigning values to each of the specific outcomes it produces. Here’s the very reasonable methodology:

BHP approximates the number of points whose outcomes were affected by the backhand: add one point for a winner or an opponent’s forced error, subtract one for an unforced error, add a half-point for a backhand that set up a winner or opponent’s error on the following shot, and subtract a half-point for a backhand that set up a winning shot from the opponent. Divide by the total number of backhands, multiply by 100*, and the result is net effect of each player’s backhand. Using shot-by-shot data from over 1,400 men’s matches logged by the Match Charting Project, we can calculate BHP for dozens of active players and many former stars.

There’s a lot to be gleaned here. For one, despite worldwide slobbering over its aesthetic perfection, Fed’s backhand posts only a +0.2 figure over his career; he does most of the damage with his serve and forehand. And as any eye test would confirm, Nadal’s topspin has a way of harassing that backhand and turning it into a liability. Sackmann isolated the Grand Slam meetings between these two players and listed Federer’s BHP in each case:

You’ll note that there’s only one time his backhand ever produced positive outcomes overall, and that was this Sunday, when he posted an anomalous +7.8 figure.

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Among the other good tidbits here: my favorite backhand on tour, Kei Nishikori’s smooth and accurate two-hander, boasts the highest BHP among top players at +3.6. The slappy backhand of Jack Sock, who makes a living on his mortar of a Western forehand, earns a sad BHP of -6.6. Looking to the past, Andre Agassi, considered a master of the shot, posted a +5.0 over his career.

Tennis is a fluid sport, yielding only a handful of sturdy analytic distinctions (forehand/backhand, crosscourt/down-the-line, groundstroke/volley), and even those can turn murky. The box score stats flashed onscreen during a match tell a reductive story, and bake in-the-moment judgment calls deeply into their core (are you sure that error was unforced? Were you reading the spin?). But thanks to some enterprising volunteers, we’re finally making some headway—you can support Sackmann’s work here.