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.