Tuesday, 24 July 2012

Soccernomics and Penalty Shootouts.

Just a quick followup to yesterday's post regarding penalty shootouts, especially as it has attracted a large number of views and quite a few emails.

To clarify, the claim that the team taking the first penalty automatically has a 60% chance of winning before a ball is kick is Soccernomics' claim, not mine. So can people please stop emailing to say it's crazy to suggest that the team shooting first has a 60% chance of winning......I know it is

Soccernomics have taken I believe 129 shootouts where the team kicking first has won 78 of the contests (60.4%) and proposed that the team opening the penalty shootout in future contests will enjoy this advantage.

I do not agree with this interpretation of their figures.

Imagine I toss a fair coin ten times and get 6 heads (60%). Could I claim that the coin is actually biased and heads will enjoy a 60% chance of appearing in future tosses? Intuitively the answer is no. I can try to confirm this intuition by either assuming that the coin is a fair one and calculate how likely I am to get an result as extreme or worse than 6 heads in 10 tosses with such a coin. The answer is 75% . That's a pretty big possibility that my 6 heads have arise by chance from a fair coin. Or I can carry on tossing to get more data.

All you can say about a series of trials is how likely or unlikely is the result if we assume the coin is fair or has varying degrees of bias. Even with 129 trials and 60% heads, we can't say that this is a 60% biased coin, we can only make claims based on likelihood and probability.

Below I've also taken option two, namely conduct more trials. I've recorded the results of just under 700 penalty shootouts, some of the data I'd previously collected, but I've updated it over the last day or so. It comprises all World Cup finals,all Euro Championships, the majority of FA Cup ties, Carling Cup ties, Asian cup matches, ACN games, playoff matches, European club ties and Johnson Paint games. Sources are many and varied, ranging from ESPN, to newspaper reports, wiki and fan uploaded Youtube video. I've read so many Brentford JP match reports, I'm halfway to becoming a fan! In many cases it is impossible to decide which team shot first, so many games have been omitted.

Success Rate of Teams Kicking First in Penalty Shootouts 1974-2012. Various Competitions.

Number Of
Penalty Shootouts.
Number Won
By Team Kicking First.
% Won By Team
Kicking First.
689 358 52

There's a 1 in 3 chances that a fair 50:50 shootout will produce 358 winning contests for the team going first in 689 attempts. Statistical convention suggests that you can start to harbour doubts when you find results that have a 1 in 20 or smaller probability of occurring by chance in a fair device.

How ever you look at penalty shootouts, a claim for a 60% future success rate for first shooters isn't supported by the numbers.

On to other matters.................


  1. Any chance this 60% thing is recent.I saw it mentioned during the shoot out in he euros,so perhaps hey are using results from the last couple of sessons.

  2. Anon,
    of the most recent 200 or so English cup games that have gone to a shootout, slightly more have been won by the team shooting second!