Wednesday 24 July 2013

Robin van Persie Really Isn't Afraid to Miss.

A year ago I wrote a couple of posts about the shooting characteristics of Robin van Persie under the general heading of "strikers shouldn't be afraid to miss". The data was from 2010/11, so the Dutchman was still an Arsenal legend, rather than a dangerous opponent from a championship seeking rival who makes a once a season visit to the Emirates stadium.

To summarize the post, when comparing the chances of a van Persie goal effort resulting in a score against location corrected efforts for the other main Arsenal shooters, the Dutchman was clearly superior. However, in terms of accuracy, it was his group of colleagues that were more likely to hit the spot and no matter where the shot originated from, van Persie was slightly more likely to miss the target completely.

I speculated that the rest of Arsenal's strikeforce was taking the mantra of "make the goalie work" to rigidly, taking less risks and more guaranteed applause by failing to shoot towards the less accessible areas of the goal for fear of missing. In short, van Persie's shot placement was more adventurous, more prone to missing the target completely, but ultimately more rewarding in terms of goals scored as a result of this efforts struck towards the periphery of the goal, generally being more difficult to save.

I intended to compare van Persie's shot placement to see if he was indeed working with finer margins, but instead the post became a general look at shot placement as well as shot power on the regularly seen location based shooting models. That post turned up last month as Power and Placement , so now is a good time to revisit the original van Persie venture.

Placement is an obvious factor in determining the outcome of a shot, although the effect of shot power is likely to have a much greater influence on the final result. From data used in the previous link, shots hit from identical pitch positions, but aimed closer to the frame of the goal, increase the likelihood of scoring. But when going from a weak to a more normally paced shot from the same spot, the improvement in expectation is generally many times greater. Shot pace is likely to be a major factor in calculating goal expectancy, but it just isn't generally available, so we will have to include placement alone, largely ignorant of the potential effect of shot power.

Although both keepers and strikers have a "natural" side, it's unlikely, given the numerous body shapes a player has to adapt to get a shot away that one top corner is very much different from the other. Therefore, to see how van Persie's shot placement may have enhanced his performance compared to a shot location based model alone I summed his total top corner, bottom corner and central attempts and saw how they compared in terms of frequency to those of similar contemporaries, namely the top scorers from all the other Premiership sides from 2008 onwards and his fellow Arsenal strikers over the same time scale. This approach also boosts sample size.

Percentage of Shots Hitting Particular Areas of the Goal, 2008/13.

Player/Team. Top Corners. Lower Corners. Top Central. Lower Central.
R. van Persie. 15% 54% 8% 23%
Arsenal exc. RvP. 12% 50% 7% 31%
League Ave.
Top Scorers
13% 50% 8% 29%

The impressions from the original post appear to be confirmed by more granular data. Robin van Persie does appear to find the top and bottom corners proportionally more often than his now former goalscoring teammates, as well as beating the pooled average of the top scorer from each permanent member of the Premiership club since 2008. Only Villa's cumulative pool of leading scorers has bested van Persie's ability to hit the corners over the last five completed seasons. For those fond of anecdotal evidence, the Dutch striker has also hit the woodwork 17 times in the last two seasons, perhaps indicating that he is likely to be shooting with an extremely narrow margin between probable glory and individual shooting failure.

By daring to miss, the premise of the original post appears sound, RvP seems to be boosting his scoring rate at the expense of his accuracy.

van Persie outperforms a simply model based around just shot location. If we then incorporate shot placement into an updated version and van Persie (or any other player) consistently outperforms that version, we need to entertain the idea of including other variables, such as shot power. And then onto defensive pressure or player movement and quality of assist. Models always fail to include every possible factor, but as long as we know what is included, they remain valuable. What's absent is the likely cause of discrepancies and this can lead to fruitful, further investigation.

Perfecting shooting models is an onion that's going to take some peeling.

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