Klaassen & Magnus's 22 Myths of Tennis - Myth 7

With the second round exit of Novak Djokovic and the quarterfinal loss of Roger Federer, the finals of the 2016 Monte Carlo Masters brought us a pairing we might not have expected on Day 1, but a thrilling one nonetheless. The first two sets between Rafael Nadal and Gael Monfils on Sunday were as tightly contested as the fans that withstood a rainy morning in Monaco could have hoped for. Each player exchanged a 7-5 win, battling through multiple long rallies and over two hours of matchplay to reach the third deciding set.

The level was so close in those first two sets that each point took on more weight than usual. The slightest slip up seemed like it could be decisive. The evenness of the play made several double faults at key moments in the match stand out to an extreme. By the end of the second set, Monfils had lost 5 points on serve due to a double fault and Nadal had lost 4. More than one of those faults gave the opponent a break of service, the most devastating being the one that gave Nadal the first set win.

Credit to Monfils for keeping his head enough in the match after that lapse to pull out a second set win.

Double faults don’t often take on as much importance as they did in the Monte Carlo final. But they never fail to provide a fascinating stage to a player’s inner game. When faced with a second serve, will the server take the risk and go for a line? play it safe? or lose their cool and tank one into a net?

Although we can never know a server’s intentions at the time they hit their serve, and whether, on a particular fault, they were knowingly taking a risk with a big second serve or just messed up, we know that a server never intends to give away a free point to their opponent. This makes the frequency of double faults a lower bound for when a server’s intentions went wrong.

Myth 7: “The probability of a double fault is the same in the men’s singles as in the women’s singles”

In myth 7 of Klaassen and Magnus' Analyzing Wimbledon, the authors were interested in whether the frequency of this service error is the same for men and women. As noted in the previous post on the percentage of serves in play, K&M found the “remarkable fact” that men and women had a frequency of double faults of approximately 5.5%, according to serve performance at Wimbledon only.

The authors also observed that the men’s double fault frequency was on the decline between 1990 and 2010, while the frequency for the women appeared stable. This complicates the conclusion about the similarity in men’s and women’s rate of double faults as it suggests that the answer depends on when you look.

Re-examining this question with a broader dataset that includes all matches of top 100 ATP and WTA players from 2006 to 2014, I found a much starker difference in the frequency of faults between tours (Figure 1). On hard and clay courts, the chance that a service point will result in a double fault has been about 5% for the WTA but closer to 3% for the ATP. A recent study by the Game Insight Group at Tennis Australia, which I pointed out last week, found the same pattern at the 2012-2014 Australian Open where WTA players had roughly twice the double faults per service point as ATP players.

The trends appear relatively stable, except for grass matchplay, where double faults are decreasing on the women’s tour and approaching the rates observed on the men’s tour.

While this analysis suggests that the story on faults has changed quite substantially since K&M dived into the question, it still leaves a lot unanswered. It might be tempting, for example, to conclude that top male players just have better accuracy on server. Possibly. But it would be hasty to jump to that conclusion before looking not only at how often faults occur for each tour but when they occur.

We know not all points in a tennis match are equally important. In some instances, a server might take strategic advantage of a “safe situation” to take a riskier second serve. You might not fault and, even if you do, you might still do something that is a winning strategy overall by keeping your opponent on their toes. Previous investigations indicate that servers are perhaps too conservative on the second serve. So perhaps a slightly higher double fault rate isn’t such a bad thing if they are on relatively inconsequential points. Maybe the question we should be asking then isn’t simply whether double faults are more frequent on the women’s tour but whether a Monfilsian fault to give up a set is more frequent.