Johnny Mac & brother Pat were talking about the awesomeness of Federer’s play tonight, and part of the discussion went something like this:

**Pat:** “I’d classify that as a forced error”

**JM:** “A forced error? Maybe, but they don’t track that stat.”

**Pat:** “No, but they should”

**JM:** “Yep. Hey, by the way, did you check out that cool article about Tencap in Tennis magazine?”

**Pat:** “Tencap? Never heard of it?”

**JM:** “You *cannot* be serious!”

[OK fine, I made that last part about Tencap up]

I don’t know whether the McEnroe brothers have heard of Tencap or not, but I’d be surprised if they haven’t heard of the “Aggressive Margin”, which is a real (derived) statistic that *does* track forced errors*. How, you ask? Simple. Check it out:

For our example, let’s take a look at Melanie Oudin’s beatdown of Savchuk through the harsh, dispassionate lens of statistics. Everything down to “Average 2nd Serve Speed” is available on the US Open website when you click on the “match statistics” link.

To calculate the forced errors, there are three things we need to know:

- The number of
*unforced*errors - The number of winners
- Total points scored

Everything else can be calculated from those stats, and a little common sense.

Back to Oudin: To calculate the number of *forced* errors she created (that is, the points she gained by forcing errors from Savchuk) we first add up her winners (20) and Savchuk’s unforced errors (15) for a total of 35 points. We then subtract this from the 55 points that Oudin scored to reveal that her other 20 points came from forced errors. Pretty simple.

Here’s the formula: Forced Errors (errors you forced your opponent to make) = Your total points minus (your winners + their unforced errors)

Taking this a step further reveals the aggressive margin. Add Oudin’s 20 winners plus her 20 forced errors together to see that she scored a total of 40 “aggressive points”. However, she gave 9 points away in unforced errors, so the margin (the aggressive margin) is 31 points. Compared to zero for Savchuk. Pretty dominating performance!

US Open Round 1 |
Oudin |
Savchuk |

1st Serve % | ||

Aces | ||

Double Faults | ||

Unforced Errors | 9 | 15 |

Winning % on 1st Serve | ||

Winning % on 2nd Serve | ||

Winners | 20 | 3 |

Receiving Points Won | ||

Break Point Conversions | ||

Net Approaches | ||

Total Points Won | 55 | 24 |

Fastest Serve Speed | ||

Average 1st Serve Speed | ||

Average 2nd Serve Speed | ||

Points scored by forcing errors | 20 | 12 |

Winners | 20 | 3 |

Aggressive Points | 40 | 15 |

Aggressive Margin | 31 | 0 |

By the way, I first read about the Aggressive Margin in the New York Times “Straight Sets” blog, in a post titled “Behind the Numbers of a Federer Victory”

“…the Aggressive Margin is…“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…”

“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 on 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.”

Also, if you’re cool with Google Docs & Spreadsheets, I’ve created a ready-made template you can use (an excel file you can download) that will automatically calculate the aggressive margin for you.

* For the record, a forced error is what happens when you hit a shot that your opponent can’t deal with. Remember the last time you were playing doubles and your partner chipped his/her service return so that the ball floated – nice, fat and slow – directly into the overhead smash pattern of your opponent at the net who, seeing a chance to end the point, crushed the overhead directly at you while you, sensibly (though feebly) raised your racquet in a defensive “self preservation” reflex, only to have the ball glance off the frame of your racquet? That was a forced error; your opponent forced you to make an error, it’s not like you had a chance of actually putting the ball back into play.

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