Who Will Win the US Open? Predicting Tennis Champions Using Grunt Pitch

New research suggests that the fundamental frequency of a tennis player’s grunt can predict match outcome.

Fans gear up for the US Open. Andreas Komodromos/Flickr

As the US Open tournament gets underway, tennis fans and sports pundits around the world are predicting who will walk away with the fourth and final Grand Slam title of 2017.

Serena Williams, who has six US Open titles to her name, has ruled herself out of contention due to pregnancy. Stan Wawrinka, who won the men’s tournament last year, has withdrawn with a knee injury. Neither of these former champions will win. So, who has the best shot at victory?

One way of predicting the winners is to look at the seeds, which are calculated by crunching stats on the players’ past performance. In the men’s world rankings, Rafael Nadal recently surpassed Andy Murray and so the Spaniard is odds-on favorite to take the US Open title. Karolína Plíšková, a finalist in 2016, is the top seed in the women’s tournament.

But what if we take less of a stats-focused “moneyball” approach and instead consider whether some players enjoy a psychological advantage?

“It is cheating, pure and simple.”

Recently, a team of scientists from the University of Sussex in the UK did just that. They decided to tackle one of the most controversial aspects of the modern game: grunting.

Serena Williams is known for her grunting, but is not competing in this year’s US Open. Edwin Martinez/Flickr

Grunting is the loud noise players make when they audibly exhale upon striking the ball. The Williams sisters, Rafael Nadal, and Novak Djokovic are all renowned for their emphatic grunting. Many grunters, including Wimbledon champion Maria Sharapova, claim that grunting comes naturally to them. But others complain that grunting is an intentional tactic, designed to psychologically intimidate the opponent. Martina Navratilova has gone so far as to state that “it is cheating, pure and simple”.

Grunting as a dominance signal

Regardless of whether grunting is a tactic or an involuntary byproduct of hitting a little yellow ball really hard, there are good reasons to suspect that the properties of a grunt might predict a match’s outcome.

In the animal kingdom, physical contests are often associated with vocalizations. For example, red deer stags roar at one another during rutting season to establish dominance; if neither male backs down, only then do they resort to clashing antlers. Male deer with deeper roars tend to be in better physical condition. Likewise, male chacma baboons produce deeper calls the higher they rise in the dominance hierarchy.

Depth of call may be related to body size when we compare between species (e.g. bats produce higher pitched calls than pandas), but differences within the same species may be due to dominant individuals experiencing greater arousal, which places the vocal folds of the larynx under tension, thereby deepening the voice.

Red deer stags produce deep roars during rutting season. Carole Ratcliffe/Flickr

To test if the same might be true of tennis pro’s, Jordan Raine and his colleagues at Sussex recorded the grunting sounds of the world’s top 30 male and female players. Then they used an audio analysis computer program to measure a property of the voices called fundamental frequency — the main factor influencing voice pitch. A tenor singer has a lower fundamental frequency than a soprano.

Grunting to win

They found that male players did produce deeper grunts than women, but that age, height, and weight were not associated with grunt depth. There was also no link between the pitch of players’ normal speaking voices and the pitch of their grunts.

Male players like 2017 top seed Rafael Nadal produce deeper grunts during matches they go on to win. Yann Caradec/Flickr

However, when the scientists compared the pitch of grunts produced during matches the players won and lost, they found that men produced deeper grunts in matches they went on to win. The trend was similar in women, but not statistically significant. The difference in pitch between winners and losers was around one semitone, or a twelfth of an octave.

This difference is audible. Raine played the grunts to a group of volunteers, who were able to identify with greater accuracy than chance which grunt was produced during a winning and which during a losing match.

Both male and female players tended to produce higher pitched grunts later in a match, possibly because when people are tired and stressed their vocalizations rise in pitch. However, winners produced deeper grunts than losers at all times during a match. This suggests that we should be able to predict the winner of a match based on the pitch of their grunt right from the first serve.

The researchers say:

Although our sample included players who grunt sufficiently frequently to allow for behavioural observation, future work may investigate predictors of variation in the occurrence of grunting both within and between players to more fully understand the mechanisms and functions of tennis grunts.

As the US Open progresses, try turning off your TV and tuning in to radio coverage. Listen closely to those sonorous grunts and have a go at predicting the victors. Assuming you’re not tone-deaf, more than half of your predictions will be correct. You might even beat the pundits!


Raine, J., Pisanski, K., & Reby, D. (2017). Tennis grunts communicate acoustic cues to sex and contest outcome. Animal Behaviour, 130, 47–55. Read summary

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