Monday 15 January 2018

Arsenal Letting in Penalties Doesn't Defy the Odds.

Arsenal fans have been getting hot under the collar about penalties.

Penalty kicks have either been awarded (against Arsenal) when they shouldn't have been, not awarded (to Arsenal) when they should have or when they have been conceded, they've gone in, alot.

The latter has spawned the inevitable trivia titbit.

There's nothing wrong with such trivia as fuel for the banter engine between fans, but almost inevitably they quickly become evidence for an underlying problem that exclusively afflicts Arsenal.

Cue the Daily Mail "why is Arsenal's penalty saving record so poor"

So lets add some context.

We're into familiar selective cutoff territory, where you pick a starting point in a sequence to make a trend appear much more extreme than it actually is.

As you'd probably guess, Arsenal saved a penalty just prior to the start of the run.

They also saved one Premier League penalty in each of the preceding two seasons, two more per season if you go back two more campaigns and obligingly opponents penalty takers also missed the target completely on a handful of other occasions.

If you shun the exclusivity of the Premier League Arsenal keepers made penalty saves in FA Cup shootouts and induced two misses in Community Shield shootouts, the latter as recently as 2017.

Over the history of the Premier League, 14% of penalties have been saved by the keeper. The remaining have gone wide, hit the post, been scored or an attempt has been made to pass the ball to a team mate. (Arsenal, again)

Arsenal's overall Premier League penalty save rate is also 14%.

So you should ask if we're simply seeing a random streak that was likely to happen to someone, not necessarily Arsenal, over the course of Premier League history.

Arsenal has conceded nearly 100 Premier League penalties because they have  had dirty defenders  been ever present, respected members of the top flight.

Of the current Premier League sides, 17 have had the opportunity to concede a run of 23 consecutive penalty goals.

If we simulate all the penalties faced by each of these teams using a generic penalty success rates, you find that at least one side during the current history of the Premier league will have conceded a run of 23 penalty goals or more in just over half of the simulations.

Letting in penalty after penalty, sometimes up to and beyond 23 is something that is going to have happened slightly more often than not in the top flight, based on save rates.

Arsenal just happen to have had both the opportunity and the luck to have been the Premier League's slightly odds on reality star winner.

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