Why Serena Williams Isn't the 700th Player By Any Measure

While tennis' top players have been spending this week making their final preparations for the upcoming 2017 Wimbledon Championships, one tennis commentator has been stirring up controversy.

In a recent interview with NPR, 7-time Grand Slam champion John McEnroe inexplicably took a shot at 23-time Major winner Serena Williams when he opined that she would be ranked only 700— a Futures-level player—if she played on the men’s tour.

McEnroe’s comments continue a string of headline-grabbing chauvinistic behavior among some of the sport’s most well-known retired players that includes Ilie Nastase and Raymond Moore. The fact that this came from one of the most popular commentators in the sport is a sad reminder that, although tennis is considered one of the most equal of sports, it still has a long way to go to eliminate gender bias.

Even more frustrating is the reality that many tennis fans are likely to agree with McEnroe’s comments, however unfounded and baseless they may be. So, as much as the rest of us would like the “Battle of the Sexes” to be a ghost of tennis' past, McEnroe’s comments have reawakened the gender debate and necessitates a response.

McEnroe’s point-of-view is based on the premise that the physicality of men’s tennis is so far superior to women’s tennis that even the undeniable GOAT of women’s tennis wouldn’t be able to make it at the tour-level.

Is there any evidence to justify this perspective?

The most obvious place to look is the serve. This is not only the most important part of the game but it is also the one skill where the physical differences between men and women are most notable. While many professional women players keep pace and even exceed men’s groundstroke speeds, their power on serve is generally 15% less than that of similarly ranked men.

But Serena Williams is another story all together. Below, I’ve compared Serena’s service speeds at the Australian Open between 2013 to 2017 against the first round men’s players in the same years, which would represent the top 100 male players on the tour. On first serve, men hit at around 180 kph on average, while Serena’s average is 170 kph, just 5% under the typical top 100 male player.

Moreover, Serena’s 90% interval directly overlaps with the top 100 male servers. This tells us that there would rarely be a Serena serve whose power wasn’t competitive with the best male players in the world.

But one could correctly argue that speed is only one ingredient of a successful serve. Placement is also critical.

As part of my role in the Game Insight Group at Tennis Australia, we have used a number of years of tracking data to create a dictionary of shots based on their speed, location, and shape. Our dictionary gives us a precise description of the distinct shots in the professional game. One of the most interesting we can do with this dictionary is to look at how often a player uses each type of shot and create a style profile from their shot “vocabulary”.

I can also see how often a female player uses the shot types in the men’s game and, in this way, determine how similar her style is to any of the male players based on the detailed physical features of her shots.

What does this method tell us about the similarity of Serena Williams' first serve style compared to top male players?

The chart below shows clusters of service styles among top male players. The closer two players are in the tree and the deeper the branch separating them, the more similar their playing styles. You can see, for example, that Roger Federer, Novak Djokovic, and Stan Wawrinka are all in the same style cluster.

Most interesting to the present story is where Serena Williams is placed. A player who could not compete with these ATP players would be an outlier even more extreme than outliers like Dudi Sela. But Williams is square in the center of a cluster that includes Andreas Seppi and Richard Gasquet, both top 20 players. This gives the most convincing rebuff of McEnroe’s assertion. Far from being a 700-level player, Serena Williams has the power and serving style that is equal to top 30 male players.

These numbers satisfyingly show that McEnroe’s comments were off base but I long for the day when rebuttals like this are no longer necessary. No one would challenge Roger Federer’s achievements because he might not be able to dunk on LeBron James. If men’s tennis is judged on its own merits, women’s tennis deserves that same.