Fact check: No shots = momentum swing?

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According to a recent Reddit-post, the momentum will swing in your favor in the 2nd half if you haven’t had any shots on goal in the 1st half. The conclusion is based on a statistical analysis, but does the numbers really check out?

The claim

Arlington69 has recorded a massive amount of data about his own matches throughout the year. He is also a proponent of the momentum theory. In his latest post, he tests the claim that the momentum will shift in your favor if you don’t have any shots in the 1st half.

This is his conclusion:

“Where I failed to have a shot on target in the first half my team showed considerable improvement in the second half reducing the clear skill gap without having an noticeable effect on the end result.”

The conclusion is based on match stats from 550 matches or more specifically the 24 cases, where Arlington69 went through the 1st half without having a single shot on target. He calculated averages for total shots, shots on target and goals per half for those 24 matches.

This is what he observed:

1st half
(total shots / on target / goals)
2nd half
(total shots / on target / goals)
Opponent average 6.79
4.05
2.04
5.63
4.04
1.79
Own average 1.00
0.00
0.00
4.88
3.46
1.29

Based on these observation, Arlington69 concludes that he improved in the 2nd half whereas his opponent performed worse. However, Arlington69 still lost 23 of the 24 matches. So, while the skill gap according to Arlington69 was closed, it apparently didn’t impact the final result.

Criticism

Cut to the bone, Arlington69 argues that something sinister must be going on when players, who perform extremely poorly in the 1st half of a football match, on average tend to perform better in the 2nd half. The problem with this line of reasoning is that Arlington69 fails to realize that his observations fit perfectly well with the circumstances you would expect to find if everything is perfectly normal.

What Arlington69 does here is to create a subset of all those matches where he didn’t take any shots on goal in the 1st half. And when you make such a subset, you per definition will see your performance improve between the two halves and relative to the opponent because your sample will include all those matches where you just happened to take all your shots in the 2nd half. But this of course isn’t due to momentum but a plain and simple product of coincidence. Sometimes, a player or a football team just happens to take all shots in one and the same half, and particularly so if the total number of shots was low.

When analyzing Arlington69’s underlying datasheet, which he shared with us earlier, we found that the scenario, where either player took all his shots in the 1st half occured in 7 % of all matches. But – not surprisingly – the opposite scenario, where either player took all his shots in the 2nd half, also occured in 7 % of the matches.

The isolated fact that players, who had 0 shots in the 1st half, oftentimes performed normally in the 2nd, may fit with the momentum narrative that Arlington69 is pushing. But if he is to extend his line of reasoning to the opposite and just as frequent scenario – players having 0 shots in the 2nd half, he would need to defend the claim that the game also swings momentum away from you when you perform normally in the first half. This is an absurd claim, not least given the fact that the by far most common scenario is that both players have shots on goal in both halves.

Conclusion

Arlington69’s experiment doesn’t suggest that there are momentum swings. This is pseudoscience at it’s worst.

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