By Ian Graham*
I have been following Soccer By The Numbers for a while, and I usually love the articles Chris writes. I took a professional interest in his article on the Uselessness of Free Kicks in the Premier League: While we were developing the Castrol Rankings, we looked at free kicks and came to the conclusion that winning a free kick increased a team's chance of scoring a goal. I had also analysed shots from free kicks, and came to the conclusion they were no bad thing.
Chris' merciless demolition of direct free kick shots alarmed me: I had to look at the data again to convince myself I'd done the right thing. So, here's my defence of free kick shots.
Chris makes the point that FK shots are rare - it's a good point, but the really interesting question is what they're worth when you have the chance to perform one (after all penalties are rare, but clearly valuable). Chris showed that most teams failed to convert any direct FKs into goals, and that most of the teams that did manage it had poor conversion rates hovering around the 5% mark.
But we can't compare direct FKs to other types of shot - they come from outside the box, by definition! So I looked at the Opta data that goes into the Castrol Rankings to try and benchmark FKs against other shots more fairly. The data set includes all shots except penalties recorded by Opta from the Premier League 10/11 season.
The results? First I found that "normal" shots from outside the box (i.e. not direct FKs) originate about 23.5 metres from the goal line, compared to 24.5 metres for direct FKs (see graph 1). I think that's close enough to say we're comparing like with like.
And when we do compare like with like, the true value of a direct FK is revealed! 4.5% of direct FKs are converted compared to only 2.6% of normal shots from outside the box. So, in an average match situation a player might nearly double his chances of scoring a goal by diving for a FK rather than taking a shot from open play.
I would say this is decent evidence that direct Free Kicks are a valuable resource. Phew. One final point of interest:
Any sort of shot outside the box is clearly rubbish compared to one from inside the box.
* Ian Graham is the head of football research at Decision Technology, based in London. Since 2005 he has developed a set of statistical models for the prediction of football matches and the rating of players. At Decision Technology Ian delivers bespoke data analysis to European clubs, providing a framework for player recruitment and squad optimization decisions. He also works with the Premier League, consulting on a number of projects. He developed the Castrol Index, a novel player rating system used in both Euro 2008 and World Cup 2010. The Castrol Rankings project generates monthly player ratings for more than 2,000 players across Europe’s best five leagues. Since 2005, he has produced statistical research and Premier League predictions for the “Fink Tank” column in the Times.
