A couple of days ago, I wrote about the positive leverage teams generate when they are up by a goal or the lousy leverage they have when they are down by one. I defined the leverage that puts one team in control of the match or creates pressure on another team statistically as “the likelihood of winning, given the score and the time remaining in the game.” For the purposes of these analyses, I measured leverage by the expected odds of winning the match, given a particular score line at halftime. The calculations showed that a halftime goal difference (GD) of +1 gives teams almost 70% leverage (defined as the odds of winning the match), while GD of -1 only provides teams with a 10% leverage level. Given that a team's overall (generic) expected frequency of winning any match prior to kickoff is in the 36-37% range, being up a goal doubles the odds of a win, while being down a goal cuts it by a factor of almost 4.
These numbers are averages calculated across 4 leagues and 5 seasons to provide a baseline to compare teams against. Once we know the baseline, the next question is, of course, which teams have leveraged leverage, so to speak; that is, which teams have outperformed historical averages, and which ones have not? So here are some leverage statistics for the Premier League this season to get a sense of how teams are doing.
The data are for teams after 27 matches. Remember from the earlier analyses that GDs of +1 and -1 are particularly meaningful and where most of the statistical action is. So here are two scenarios: first, leverage from a +1 GD; second, leverage from a -1 GD. So here's first the +1 GD analysis.
These numbers are averages calculated across 4 leagues and 5 seasons to provide a baseline to compare teams against. Once we know the baseline, the next question is, of course, which teams have leveraged leverage, so to speak; that is, which teams have outperformed historical averages, and which ones have not? So here are some leverage statistics for the Premier League this season to get a sense of how teams are doing.
The data are for teams after 27 matches. Remember from the earlier analyses that GDs of +1 and -1 are particularly meaningful and where most of the statistical action is. So here are two scenarios: first, leverage from a +1 GD; second, leverage from a -1 GD. So here's first the +1 GD analysis.
The +1 GD scenario shows huge variation across the league, from 1 in the case of West Brom and Stoke to 0 in the case of Wigan. The league leaders (in this order) were West Brom and Stoke, followed by Manchester United, and then tied for third we had Sunderland, Newcastle, Man City, Chelsea, and Bolton. Considering that the long-term historical leverage in a +1 situation is .69 (so roughly 70%), the underperforming teams include (starting with the worst underperformer of the league) Wigan, Liverpool, Everton, Wolves, Birmingham, Fulham, Aston Villa, and West Ham. There are no real surprises in this group, except perhaps Liverpool.
Of course, it's important to keep in mind that the frequency with which teams are in the advantageous position of having positive leverage varies quite a bit: league leaders West Brom and Stoke who had a perfect leverage score only had 3 matches with a +1 GD at the half. In contrast, Manchester United who are a close third at over .9 had 11 matches where they were up by one goal at the half.
Of course, it's important to keep in mind that the frequency with which teams are in the advantageous position of having positive leverage varies quite a bit: league leaders West Brom and Stoke who had a perfect leverage score only had 3 matches with a +1 GD at the half. In contrast, Manchester United who are a close third at over .9 had 11 matches where they were up by one goal at the half.
So what about negative leverage situations, defined here as a -1 GD at the half?
Turns out, only six EPL teams have positive leverage values this season when the goal differential is -1: Tottenham, Arsenal, Liverpool, Stoke, West Brom, and Fulham. The rest have a leverage score of 0 in a -1 GD situation. The leverage leader from a defensive leverage position has been Tottenham (at .4 and thus roughly four times the historical average of .1 across leagues), followed by Arsenal and Liverpool at around .25 and .2, respectively. And all teams with positive leverage exceed the historical average.
So Liverpool and Fulham make up for some of their underperformance on the +1 GD shown before, and West Brom and Stoke are yet again in positive territory. For teams like Stoke and West Brom, their leverage has real value: by the end of February, West Brom had been in -1 GD territory 8 times, and Stoke an amazing 11 times. Contrast that with Manchester United who only were in that position once.
So Liverpool and Fulham make up for some of their underperformance on the +1 GD shown before, and West Brom and Stoke are yet again in positive territory. For teams like Stoke and West Brom, their leverage has real value: by the end of February, West Brom had been in -1 GD territory 8 times, and Stoke an amazing 11 times. Contrast that with Manchester United who only were in that position once.
So according to these calculations, Stoke and West Brom look like the league's leverage leaders so far this season. Pretty amazing, if you ask me.
