Net Approaches in Pro Tennis: A New Analysis

How statistically effective is playing the net really? Is playing the net more effective than staying at the baseline? The simplest method to answer this question is to compare win probabilities at the net versus at the baseline. In the final section of his brilliant article on the New Magic Numbers, Craig O'Shannessy reports that players won 65% of their approaches in his studies at the U.S. Open, and that this percentage was almost as high at every level, from 12 and unders up through college tennis. (Click Here.) However, my research shows this method is insufficient to make a truly accurate determination. Why? Because win probabilities at net can be deceptively high. When using statistics to determine the effectiveness of playing the net, it's essential to account for other relevant variables--not just win probabilities. For instance, many approach shots are hit off easy balls, which give you an advantage in winning the point irrespective of whether you approach the net or not. Suppose you serve four points. Twice, the returner floats the return, and you approach the net and put away easy volleys. But the other two points, the returner hammers the return and forces you to play defense....