Wimbledon: What the data says about some tennis 'myths'

By Rob HaywoodBBC Sport
Novak Djokovic serving
Do new balls help the player who is serving? And are you more likely to serve an ace on game point?
Wimbledon 2022 on the BBC
Venue: All England Club Dates: 27 June-10 July
Coverage: Live across BBC TV, radio and online with extensive coverage on BBC iPlayer, Red Button, Connected TVs and mobile app.

During the first set of the first match at Wimbledon next week, the commentator will invariably mention that the server will be using the 'new balls'.

After the opening seven games, and then after every nine more, the old balls are removed and replaced by new ones. The popular opinion is that the new, firmer balls, give an immediate advantage to the server, something that diminishes game by game until they are replaced.

But is this true?

Dutch professors Franc Klaassen and Jan R. Magnus decided to find out if it was and set about examining as many tennis 'myths' as they could.

"The list [of myths] originated from watching tennis on TV and listening to commentators," Professor Klaassen explains. "And we combined it with our own extensive experience as tennis players."

What followed was 25 years of research, academic papers and a book.

The initial work included data from 86,298 points played at Wimbledon and expanded to well over 100,000 points played at other Grand Slam events, with data gathered from the 1990s up until the present day.

So what did they find and will it make us watch the game in a different way?

The myth: All points are equal

One of the fundamental questions, which followed on from research that dated back to the 1970s, was whether or not points are independent of each other.

Does the previous point have any influence on the one being played now?

The findings were clear and they confirmed that all points are not equal, although the difference between them is small.

This information was paired with the idea that an ace could be worth more than one point. The prevailing wisdom was that serving an ace gave the server so much more confidence that they would be more likely to win the next point.

The data showed that in men's singles there was an effect and following an ace the server was more likely to win the following point to the tune of the ace being worth 1.04 points, and in women's singles the effect was worth 1.01 points.

These margins are small, but sometimes that is enough to change the outcome of a point and so a game, and ultimately a match.

The myth: The seventh game of the set is the most important

If points aren't equal, what about games?

The professors knew that legendary BBC commentator Dan Maskell would often say that the seventh game of a set was the most important one, and whoever won it would be most likely to win the set.

That was found to be untrue, and that the most important games are numbers 11, 12 and 13 (the tie-break) if the set goes that far.

The seventh game could come with the scores at 5-1, 4-2, 3-3, 2-4 or 1-5. You might think that at 3-3 the seventh game is important, but data shows that it isn't. In fact the seventh game has less bearing on the set than the sixth.

The professors came up with an "importance" measure to rank each game 1-100. Game six scored 43.0 in men's singles and 41.3 in women's, while game seven scored 37.6 in men's and 36.6 in women's.

The "importance" was the probability that the server in that game wins the set given that they win the game, minus the probability that the server wins the set given that they lose the game.

The myth: Players are likely to lose serve as soon as they have broken their opponents

Klaassen and Magnus analysed what happens at the 'big points' and chose break points and game points to consider.

They found that in both men's and women's singles, the number of aces went up at game point but so did the number of double faults.

The outcome was that the total points won on serve at game point was slightly less than at all other points. Men's servers won 62.2% of points at break point compared to 65% of all points, while women won 53.5% at break point compared to 56.4% of all points. .

When game point is match point, or even Championship point, the stakes are obviously higher.

The increased aces and double faults at this point were never more tense than at the end of the 2001 final between Goran Ivanisevic and Pat Rafter. The big-serving Croat led 8-7 in the fifth set but served two aces and three double faults at crucial moments before finally capturing the crown in his fourth final.

At break point players serve fewer aces, taking more care to make sure they get the ball in play and playing more cautiously.

So does a player who wins a break of serve, relax and the player who has just been broken try extra hard to mean that a break-back happens right away?

The answer was no. Overall a player is more likely to hold their own service having made a break.

Men are 81.8% likely to hold serve, which rises to 83.3% after a break. For women, it's 64.3% normally and rising to 68.3% after a break.

Aces and double faults at game point
Aces at game point10.9%4.2%
Aces at all points9.1%3.3%
Double faults at game point5.7%5.3%
Double faults at all points5.5%5%

The myth: Whoever wins the fourth set is most likely to win the fifth

Having previously looked at the effect of a point on the next one, they looked at the effect of winning a game on the following one.

Do players gain momentum, or as they called it, a 'winning mood'?

This was the most surprising finding.

"The winning mood is much smaller than we thought it would be," explains Professor Klaassen. "Yes, there is momentum, doing well at recent points signals that the player will also do well at the current point. But this momentum is small."

How would this translate to the thinking that a player who wins a set to even a match and require a decisive fifth (men's) or third (women's) set, would they have the advantage?

The data was split into seeds and non-seeds and gave clear results.

When two seeds play, the winner of the fourth set most probably loses the fifth (an 11.1% probability of the same player winning sets four and five).

But when two non-seeds play it's the opposite as the winner of the fourth is most likely to also win the fifth (a 60% chance of the same player winning sets four and five).

When a seed plays a non-seed the winner of the fourth set is irrelevant as the seeded player is more likely to win the final set no matter what happened before (an 80% probability of the seed winning sets four and five).

These figures are the same for women going into a third set.

Looking at the 20 men's Wimbledon finals since the millennium, six have gone the distance to five sets. In every one, the player who won the fourth set to draw level, then lost the fifth.

Twice Roger Federer triumphed this way (2007 v Nadal and 2009 v Roddick), but three times he lost (2008 v Nadal and 2014 and 2019 v Djokovic).

The myth: It's an advantage to serve with new balls

The data helps to explain a lot about what happens in tennis, but what about the new balls?

Klaassen and Magnus found that slightly more aces are served by men when using the new balls (10% with new balls, 9.1% when not), but alongside this there is an increase in double faults (5.9% with new balls, 5.5% without).

So the new balls go faster to produce the aces but are harder to control, hence the double faults.

It isn't an easy answer, there are shades of grey. However, when the commentator reminds us that the server has the new balls, we do know that 'something' is going to happen more than usual.

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