Michael Caley has written an excellent series of posts recently on loking at identifying shooting skill in the Premiership, and whether there are specific players that an identifiable amount of it. One piece in particular that caught my eye is this one.

I think Michael and I think about shooting skill in a similar way – it’s something that exists (though the magnitude of it’s effect is open to debate) but over the course of a Premiership season it’s very tough to identify because players don’t take a large enough number of shots. Even teams take so few shots that their shooting percentage will regress ~60% of the way towards the mean from season to season.

In the piece linked in the introduction Michael has taken non-penalty shots from the ’09-10, ’12-13 seasons, adjusted the shots for each player based on the location of the shot, the type of shot, and the type of pass that assisted the shot. He’s then split players into two groups – shooters and non-shooters, with shooters being those who’d taken more than 38 shots over the course of the season (n.b. the original post says ‘more than a shot per game’ – I’ve confirmed with Michael that it’s >38 shots in the season, regardless of games played).

The results? Well Michael explains it best, so I’ve taken an excerpt directly from the post:

Now that’s pretty damn interesting, and I was wondering whether it’s something I can confirm. Fortunately I have a set of data provided to me by Infostrada (twitter, website) that provides me as independent a set of shots as is possible – penalties. This is something that I wrote about extensively in 2012 – a summary of which can be found here – but it’d be great to test this dataset against Michaels’ results.

From the numbers I have there are three seasons common to both mine and Michaels datasets – ’09-10, ’10-11, and ’11-12. Michael was kind enough to send me the list of ‘shooters’ in each season (for those interested they’re included in the appendix at the end of this post). I split the penalties in each season into those taken by the ‘shooters’ and ‘non-shooters’, as defined by Michael, and looked at the conversion rates of each of the two groups. The results are summarised below – first by looking at all players, then split into the two groups:

Now that’s interesting – in two of the three seasons the ‘non shooters’ have had a markedly higher conversion rate than that of the ‘shooters’, and in the third season it’s basically a wash. This looks to be showing the opposite of that found by Michael, but is it a significant finding? Below I’ve summarised the p-value of the two groups of penalties in each season, and across all three seasons combined:

So for those unfamiliar with p-values they determine how similar two groups of numbers are – and range from 0 (two groups that are entirely dissimilar) and 1 (two groups that are exactly the same). A p-value below 0.05 is considered to show that two groups of numbers are different to a statistically significant level.

As such, given the sets of penalties and their relative sample sizes this is something we’d expect to see happen about 12% of the time, and isn’t an effect that we’d call statistically significant. It doesn’t mean it’s necessarily something we shouldn’t be trying to explain though – can anyone suggest a reason as to why we’d see some players being statistically significantly better at converting almost all other types of shots, but not the one shot that is as damn close to a neutral shot as we’ll find?

**Appendix**

List of shooters in each season studied – click for a larger view:

My guess being this:

The penalty data suggests that when it is the shooter trying to beat the keeper then they win around 70-80% of the time. I can’t find the data now but shots from around the same area in-game are converted at a much lower rate. So this means that it’s about more than just shooting and beating the keeper.

It’s about getting a clear shot, good balance, composure, shooting whilst running etc.

If you are really good at all of these but 10% less good at shooting I imagine you will still have a better conversion rate than someone who is slow, panics and snatches at shots but is a better ‘shooter’ from the spot.

I guess what I’m saying is that your ability to find space, take a shot under-pressure whilst moving (and probably about to be tackled) is the dominant factor. After you take all that away (i.e. penalties) it comes down to just shooting and the leaders could well be different.

What do you think?

I agree with ability to find space being really important – I actually think that’s the majority of what teams are paying for when they buy the best strikers, but I’m not sure I follow the rest of the argument.

Well, there is certainly a chance that a dead-ball shot requires more mental energy than skill. In-game shots are mostly taken too quickly for temperament to play an important part, with the obvious exclusions of one-on-one situations. So it could be that the main skill of taking a penalty is temperament, which is less required for in-game shots.

That still does not explain why non-shooters are *better* than the shooters. My guess is that there is a selection-bias. The shooters tend to get to take penalties regardless of demonstrated temperament/success. The non-shooters who are given penalty duties are given them on the basis of demonstrated success. Actually this could well be enough without the proceeding argument.

Here’s one possible explanation:

One assumes that all keepers study (or have been told) penalty takers’ tendencies. Those would be clearer for players who take a large number of penalties, and penalty takers come from the shooter category far more often than from the non-shooter category. Thus: keepers know shooters better than they know non-shooters.

Since everyone, even the worst non-shooter, has practiced thousands of penalties, it may be that the takers’ skill gap is smaller than this keeper knowledge gap. In that case, an unexpected taker would be more likely to succeed than a good shooter.

If this were the case we’d see a negative trend in the first plot here (you could maybe make an counter argument involving survivorship bias) https://jameswgrayson.wordpress.com/2012/06/19/penalties-are-any-players-good-at-taking-them-how-about-saving-them/

However, if this were the case you’d also expect the penalty takers themselves to study where the ‘keeper dives on penalties. ‘keepers face far more penalties than penalty takers take (there’s only one person per team eligible to save a penalty, whilst there are multiple people wanting to take a penalty) so we’d expect them to be really well studied – and this effect negated.

Non-shooters do not get to take penalties unless they are particularly good at them? Put another way, perhaps non-shooters are not typically given penalty duties by default, only a select few who have demonstrated particular prowess, in training or whatever. In situations, say when the usual penalty taker is not on the field, the default is possibly often one of the strikers who is assumed to be a better shout than a defender.