Understanding Match Statistics
The Aggressive Margin

John Yandell

Still Photos by J. Gregory Swendsen

If a tennis player wants to gain a real understanding of his wins and loses in competitive match play, he needs to understand how he wins and loses points from a quantitative, or statistical perspective.

In the first article in this series, we explained the critical role of the forced error in understanding match statistics. This article introduces another key statistic, the "Aggressive Margin."

Andre Agassi has the games best groundstrokes but his Aggressive Margin is the key to understanding why he wins or loses against Sampras

Let's see what the Aggressive Margin is and what it tells us about the classic Sampras/Agassi confrontation at the 2001 U.S. Open. Then we'll compare that to the margin in some of their other classic match ups over the years. In a future article, we'll see how it illuminates who wins and loses at other levels of play.

The Aggressive Margin was first developed decades ago by the father of modern tennis statistics, Bill Jacobsen. It's a composite statistic that combines how a player wins and loses all points into a single index. Understanding this one key number allows any player to see exactly what happened in a given match, and how.

Basically all tennis points end in one of three ways: winners, unforced errors, or forced errors. The Aggressive Margin puts all three together into a comparative measure. This is one reason why it's so important to chart the forced errors-without them, it's impossible to measure the Aggressive Margin.

So how do we calculate the Aggressive Margin? First for a given player, we add up the total points won through winners and the total points won through forced errors. Then we subtract the total number of unforced errors. The difference is the margin of points the player won by aggressive play. This is "The Aggressive Margin."