Blog 2: Expected goals makes football ready for statistics

Night after night, we are treated to football experts manning the talk show table. Very entertaining and because of the football humor wonderfully accessible. If a player loses the ball three times in the summary, he is suddenly no good and the next bad bargain is a fact. Because the gentlemen look at each other a lot, other football tables take over in a flash and it is a fact: this player is a total failure.

Nowadays, however, comprehensive statistics are available for almost all players. Mileage, pass accuracy, pass direction, runs, dribbles, passes, assists. All statistics that can support the strength of a player. Yet analysts hardly look at them. While to a large extent it objectifies the performance of a player.

Now there is a relatively new statistic that says a lot about the true balance of power in a match: the expected goals. In a few years’ time this statistic has taken the football world by storm. Expected goals is a value that indicates whether a goal attempt results in a goal. It does this by crunching data from thousands of historic shots and filtering it according to factors such as distance, type of shot, type of pass and the number of defenders between the player and the goal. All this information is used to create an average percentage chance that a particular shot will go in, taking all these factors into account. This statistic shows whether the statement "Luuk de Jong should have scored this one" is true.

This is going to objectify football on two levels: team level and individual. The best example is Juventus in 2015-16. They started the Serie A season poorly. They won only three of their first 10 games, but their expected goals stats were excellent. They dominated most of their games, created many chances, but were not rewarded with victories. The Old Lady continued their chosen path, their luck finally turned, and they won 15 games in a row. At the end of the season, they were champions with nine points ahead of the follow up. Most clubs would have panicked and fired the coach. However, it would clearly have been the wrong decision to sack coach Allegri and the expected goals were an indication of that.

In addition to comparing a team's expected goals, we can see which players hits the target. If a player exceeds his expected goals, this suggests that he is lucky or a great finisher. If a player exceeds his expected goals for a few games and is not known as a super striker (like Giakomakis at VVV), he is probably on a hot streak that will not last forever. But someone like Dusan Tadic, who scores more goals than the chances he gets year in year out, is clearly an above-average finisher.

Yet analysts have a hard time with this. For example, expected goal-scoring figures for individual matches are useless without context. If a team scores a few early goals on difficult chances and then protects their lead, they affect the statistic negatively. If their opponent then gets a higher expected goal statistic because they take a lot of low quality (distance) shots, it does not mean they deserved to win the match.

Besides, football is emotion: if their team has lost, many fans are not interested in hearing television experts say that they should have scored more based on the expected goals. After all, it is not worth any points.

At those moments, football fans would rather listen to the football experts at the talk show tables than to statisticians! 

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