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Klaassen & Magnus's 22 Myths of Tennis— Myth 4

The fourth myth in the countdown of Klaassen and Magnus’s 22 myths of tennis is the myth of the seventh game. Listen to enough tennis commentary or read through enough posts on tennis forums and you are bound to come across the idea that the seventh game is the most important game in the set.

As K&M note in Analyzing Wimbledon, one of the biggest proponents of this idea was famed “voice of tennis” Dan Maskell. Throughout his long career commentating on tennis matches for the BBC, Maskell would often talk about the “crucial seventh game”. Maskell’s obsession with the seventh game was so extreme that he is remembered as much for it as for his famous “Oh, I say!”. Even in a brief retrospective, The Guardian couldn’t help but comment on this obsession, noting that Maskell was “strangely fixated on the seventh game of the set, which he never failed to label ‘all-important’”.

Maskell’s fixation might have seemed strange at the time but it wouldn’t be by today’s standards. Many current commentators and tennis fans believe in the importance of the seventh game. Just search Twitter for “all important 7th game” and you will find plenty of evidence of the broad acceptance of this belief.

Why the All Importance of the Seventh Game is Wrong

There is one simple argument that raises a giant red flag about the importance of the seventh game: the seventh game rarely decides the set. There are two ways a player can be in a set-deciding position at the 7th game, at 5-1 or 1-5, but three are 7 total game seven situations, 5-1, 4-2, 3-3, 2-4, and 1-5. Looking at the score situations for each game in a set based on 4,300 ATP matches in 2014 and 2015, we see below (Figure 1) that the outcome of the seventh game will decide the set only 15% of the time, which means that the 4-2/2-4 and 3-3 situations are much more common than the set-deciding ones.

But is the Seventh Game Predictive of the Set Winner?

Believers in the seventh game would likely counter the above argument by saying that, while the seventh game might not often decide the winner of the set it is often predictive of the winner of the set. Yet a number of analyses strongly suggest that the seventh game isn’t particularly special when it comes to winning. K&M did some calculations that showed that the importance for games 1 thru 9 was approximately 30%, given the game was reached. This tells us that winning any game gives the player an advantage for winning the set but the advantage is the same up until you get to the game situations that can decide the set.

But perhaps K&M missed something by assuming that the server’s chance of winning a point is constant throughout the set. After all, defenses of the seventh game myth often hinge on momentum. The momentum theory says that winning the seventh game gives the winner some boost, which would make their chance of winning points from that game on more likely than if they had lost the seventh game.

Is there any evidence of such order-specific momentum? Figure 2 above looks at the observed advantage of games 1 thru 9 for ATP 2014-2015 matches, always from the perspective of the higher-ranked player at the start of the match.

Because this is based on real data, it would allow for momentum effects, if they in fact occur. However, we see that the observed advantage for winning the set for each game win situation is very close to what was predicted by K&M. Importantly, the overlapping confidence intervals (99% intervals, in this case) show that the game order does not appear to have mattered for a player’s chances of winning the set in recent seasons.

What About Close Sets?

In the above analysis, I didn’t make any exceptions for the score, only the game number. Perhaps the mythology around the seventh game is only concerned with close sets. Consider this tweet during today’s Indian Wells semifinal between Novak Djokovic and Rafael Nadal. After an exchange of breaks, both players went into the 7th game with 3 games on the scoreboard. Nadal served to hold, winning a “huge 7th game”, as Tennis TV called it. Although the implication of this would seem to be that Nadal had the edge, he went on to lose the set in a tiebreak.

What do we find if we look at the role of game order in close sets for many matches? Using the ATP 2014-2015 dataset and considering only the odd games when each player had an equal number of games won at the start, the advantage for the higher-ranked player winning the set shrinks from around 30% to 10%, but the conclusion about game order remains the same (Figure 3 below).

Jeff Sackmann did an analysis on Heavy Topspin addressing the same question, which came to the same conclusion. There is nothing special about the seventh game.

Are Breaks of Service More Common in the Seventh Game?

Before concluding that the seventh-game myth has been debunked, I should also consider breaks of service. So far we have seen that the intuition about the all-importance of the seventh game does not hold up overall or in close sets. Yet, perhaps players are more motivated to break service if they are returning in the seventh game.

To see if this is the case, I plotted the frequency of breaks of service for all games except up to a tiebreak situation. Figure 4 below shows that the frequency of breaks for the ATP is about 20-21% for games 1 thru 9. So, once again, a seventh-game effect cannot be found.

The Persistence of the Myth of the Seventh Game

It would be interesting to see a history of the seventh-game obsession. Was it Maskell’s invention? or was it handed-down to him? and how did he hold on to the belief for long and with such conviction?

Since his lifetime, there have been many analyses (and more thorough than the ones presented here) that have made a strong case against the importance of the seventh game. I have put links to some of them above. Despite the evidence to the contrary, the importance of game seven continues to be a fixed idea in tennis. This might be one of those examples where the gap between analysts and commentators is most evident.

The day when skepticism about the importance of the seventh game becomes the norm among tennis commentators will be a day for tennis analytics to celebrate.

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