Monday, May 30, 2011

How Much Football Is There In A Match?

Talk in the aftermath of the Barcelona - Manchester match about who had more passes and more possession (or more this, that, and the other thing, as is often the case after matches) reminded me of The Guardian's statistical review of the Premier League's season (courtesy of Opta data). I thought one of the more interesting tidbits was that, on average, "the ball was in play for 62.39 minutes this season – more than in the much-vaunted Spanish and German top flights (61.48 minutes and 61.22 minutes respectively), but significantly less than in Serie A (65.15 minutes)."

What the comparison doesn't mention explicitly is (the perhaps obvious) that 90 minutes of a football match actually don't give you 90 minutes of football. Of course, we've all known this, at least intuitively, but it's good to know exactly how much or how little football there is in a match, for at least two reasons. First, it's good to separate fact from fiction. Second, it's interesting to think about the implications of the fact that a football match only has about an hour of actual football. Mind you, that's very different from, say, ice hockey or basketball. Hockey games are 60 minutes long and basketball games are 48 minutes long. Every time, to the 10th of a second. The puck or ball leaves the field, the clock stops. Not so in football, and I bet it matters in a number of ways.

Consider leagues, for example. Knowing how much actual football there is in a match could have implications for how we think about players' and teams' performance. If leagues differ systematically in the amount of time the ball is actually in play, we may have to reconsider whether the number of goals scored or shots taken are due to differences in quality or style of play or simply the quantity of play. So scoring a goal in a league that plays more actual football may be the equivalent of scoring .9 goals in a league that plays less. Of course, absent further and more systematic analysis, it's hard to know but intriguing to think about nonetheless. Serie A played the most minutes of football, but the league doesn't see as many goals as the Bundesliga or La Liga, for example. What do we make of that?

The Guardian also gave us a nice intuitive example for how the variation in minutes could matter for individual teams. We may love or hate Stoke's strategy of using long throw ins, but guess what? It appears to significantly reduce the amount of time the ball is in play. According to The Guardian, "the average amount of time that the ball was in play for Stoke games this season was 58.52 minutes. Manchester United offered the most action, 66.58 minutes on average." From what I know, there are matches that come close to only 45 minutes of play.

How can teams use the clock? Again, Stoke provides a good example. Not only did they try to use long throw ins to their advantage - we can debate whether they made good use of the astonishing and league-topping 550 times they did so - doing so did something else for Stoke: it reduced the other team's chances of getting hold of the ball. If you're Stoke, this could matter hugely; after all, they averaged less possession (38%) than anyone else this season, according to the analysis. So, the shorter the actual match, the better for Stoke. So throw ins kill two birds with one stone: they help create chances and shorten the match.

You may think that a minute here and there doesn't matter. I'd argue it does. The difference between Man U and Stoke in average minutes with the ball in play is 8 full minutes. As we know, lots can happen in 480 seconds. Given teams' differences in match times, some have proposed changing football's rules to stop the clock when the ball is dead. Surely, many would consider this to be the fair thing to do? But of course, it also would take one more arrow out of managers' quivers and change the way the game has been played, and that's always a tough proposition when it comes to reforming the game.