As I said in my first article on this topic I think that Ted Knutson from StatsBomb has a good idea. Individual player’s stats are deceptive and need to be grounded in the context of the “personality” of the team he plays for and the League he plays in. The idea of adjusting individual’s stats for the personality of the team, in his formula he used possession, is solid. The problem is that possession doesn’t map to defensive stats because possession is simply a ratio of passes.
The reality of football is that teams vary wildly in terms of their defensive aggression. How often a team attempts tackles or gathers interceptions has a very weak correlation to possession stats. I want to be clear that I’m not trying to hammer anyone here. Rather, I’m trying to build on Ted’s idea and create a new model which will help us to understand individual player’s stats better.
To that end, take a look at the chart of Premier League teams below (click to embiggen):
In this chart I have sorted the 20 League teams by possession. I have broken down each team’s tackles and interceptions. Then I have taken the League averages for the tackles and interceptions (added together) and the averages for tackles and interceptions. Then I have done a +/- over the average for total, tackles, and interceptions.
What you can see very clearly is that the top five teams who dominate possession also are among the most aggressive defensive teams in the Premier League, with the exception of Arsenal who are essentially an average defensive team. Those top five teams are making more passes than average (that’s what possession measures) and more tackles+interceptions than average. The next three teams are known as defensive teams and yet they have fewer tackles+interceptions numbers than average.
I think that the Chelsea numbers are a good clue as to why teams who have a reputation for boring and defensive football also are less active defensively. If you look at the whole chart, teams with a negative overall defensive number are all well known to be disciplined defensive sides. They aren’t diving into tackles or playing the passing lanes. They sit back, in two banks of four, and play positional defense. That’s my theory anyway.
So, perhaps we could adjust player’s stats based on an overall “defensive aggression” number? Even if we did that, however, we might be wrong adjusting certain player’s stats, like say tackles, on a team like Swansea who (as you can see from the chart) aren’t a very tackle oriented team.
Looking at the next two columns we see a further breakdown of each team’s defensive personality. For example, the most aggressive tackling teams are Stoke, Liverpool, Crystal Palace, Southampton, and Manchester City. I think that’s a fair assessment of the Premier League, actually. Stoke and Liverpool play smash-mouth football, which may offend some Liverpool fans but for anyone who has seen them play you know that they are scrappy and a bit dirty on the defensive end. Crystal Palace is another interesting team. I bet they avoided relegation last year simply with their amazing defensive work rate, that +299 with + in both tackles and interceptions is really crazy.
Regardless of whether you agree about my analysis of Liverpool and Crystal Palace, I think I’ve made my point here with regards to using possession as a means of adjusting player’s stats. Instead we should probably be looking at the personality of the team and using that to adjust a player’s stats. How, exactly, we adjust for that I haven’t figured out yet. I don’t have a math genius here to bounce ideas off of, like Ted does. If you’re a math wiz and you want to help, just leave me a comment below. I’ll get back to you.
In the mean-time, one more thing to consider: a team’s stats also vary from league to league. For example, the Bundesliga is a far more aggressive league in terms of tackles than the Premier League.
Remember that Bundesliga teams only play 34 games a season and yet they are averaging 339 more tackles per season than their Premier League rivals! That’s 10 more tackles a game. Per team. For my money that seems like a much more important thing to adjust for than possession.
How do we do that? I don’t know, yet!