How low can you go: Assorted thoughts about crosses
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There is a pass that David Silva and Mesut Ozil, Premier League's outstanding playmakers, are very fond of. Standing just inside the opposition penalty area close to a corner, with options inside and outside the box, they slip the ball instead to the overlapping fullback who crosses it in. Why do they do this if, as the common wisdom has it, crossing is low percentage play?
The obvious answer is that not all crosses are equal, and with good setup play a cross is a dangerous weapon. I think it is particularly true of short, low crosses, precisely the kind Ozil and Silva encourage. I set out to investigate this hypothesis, only to realise that I don't have a clean way of separating low and high crosses in my database. What follows are two simple analyses trying to work around this problem.
Completion and conversion
Two definitions: I consider a cross completed if the next on-the-ball action is performed by the player from the crossing team. A cross is converted if the crossing team scores within 5 seconds of the cross. This is an arbitrary window, but it should catch all the goals (including own goals) which are "due" to the cross in significant degree. This will include own goals, rebounds and goals from brief goal-line scrambles. Note that conversion and completion are independent in this formulation: a completed cross may be converted or not, and a converted cross needn't have been completed. I looked at the last four full seasons of the five big European leagues and only considered locations where I have more than 1000 attempted crosses. Unless indicated otherwise, only open-play crosses were considered.
As expected, the premium crossing area is on the edge of the penalty and inside it (shall we call it the Zabaleta Zone?), where around 5% of crosses are converted. If this sounds low, then consider that the average cross conversion rate is just 1.76%. What was a bit of surprise to me is that it seems to be easier to complete a cross from the wide areas, farther away from the box. I suspect this is due to the fact that with a short cross the area is on average more crowded and who takes the next touch becomes more random. Average completion across all areas is 23.58%.
Crossing and success
There is a weak positive relationship between success (measured in points per game) and the proportion of cross-assisted shots that aren't headers. (Here assist is taken in the strict sense and not in the sense of conversion defined above.) The correlation coefficient for the attached graphic is 0.43, which drops to 0.32 when Manchester City, the ultimate low-crossing team, are removed. Interestingly, this relationship doesn't exist in the Bundesliga and Ligue 1.
I don't want to speculate on the nature of this relationship beyond what Devin Pleuler said on Twitter on Monday:
That is, a preference for low crossing will come naturally to better teams.
Success and reliance on crosses are inversely related: the higher proportion of a team's shots come from crosses, the lower points-per-game. The strength of this relationship is similar to the previous, and, once again the effect is not
found in Germany or France.
There can be no firm conclusions until I find a way of separating low crosses from the rest. However, it does appear that not all crosses are equal, and that a team that relies heavily on crosses for chance creation should make sure they know what they're doing.
Data provided by Opta.