Bundesliga

Toward a model of adjusting player stats for the “personality” of the team and the league

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):

defense

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.

BundesligaRemember 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!

Qq

 

 

Possession

Why we shouldn’t adjust defensive stats for possession

“Have you thought about adjusting your stats for possession?” – Everyone since June

Last month the venerable Ted Knutson published an article strongly suggesting that us stats folks should adjust basic defensive stats like tackles and interceptions for possession. The theory being that the more possession (offense) a team owns the fewer opportunities that same team has to make defensive actions. If true, then we should adjust player’s individual stats for their team’s possession. It’s a good theory with only two minor flaws: 1) it’s wrong and 2) it’s wrong. I know technically that is just one flaw but it seems like such a big flaw that I felt it deserved to be repeated.

First, you have to understand what possession is and how it is measured. Opta measures possession simply as a ratio of passes between teams. Ergo if Arsenal make 600 passes and West Ham make 400 passes the possession numbers at the end of the game are reported as 60-40. Measuring possession as pass ratio has caused a good bit of consternation among stats nerds for a few years now. As you know, many teams, like West Ham, intentionally waste time when they have the ball in order to prevent teams like Arsenal playing. At the end of a match like that, however, a team with faster passing might end up dominating possession as something like 70-30 when in actuality the possession numbers were more like 50-40-30 with 30% of the ball being out of play.

Don’t believe me that a ball could be out of play for 30% of the match? Well, if we use the alternate method of tracking possession, the “chess method” where a clock is actually deployed and time measured for when a team has control of the ball we see that Bayern, for example, led the Champions League in possession last season at 65% and yet only had, on average, 38 minutes of play. 65% of 90 is 58.5. Where did the other 20 minutes go? Time wasting and other tactics to slow the game down.

But even if we were to accept the idea that possession is a “good enough” measure of offensive dominance and thus defensive opportunity it still doesn’t explain why a team like Barcelona who routinely have 68%+ of possession would wrack up fewer tackles than a team like West Ham who routinely have ~40% of possession. If the idea that less possession = more opportunity and therefore inflated individual and team defensive stats we should see West Ham, Fulham, and Crystal Palace blowing away teams like Barcelona in terms of total tackles and interceptions.

Or even if we were to stay in the Premier League and take Southampton, who led the Premier League in possession, and compare them to the bottom teams we should see the bottom teams have more tackles and interceptions. After all, they have more opportunity.

But rather than seeing a direct correlation between possession and defensive stats, we actually get a very poor correlation as you can see below. Southampton and Man City led the League in possession while West Ham, Crystal Palace, and Fulham were the bottom three in possession.

Possession

Courtesy http://www.squawka.com/comparison-matrix

How is it possible that Southampton made 1802 attempted tackles and interceptions while West Ham, a team known as a tough tackling side who Stuart Robson loves to commend for “earning the right to play”, makes just 1456 of the same actions? That’s 346 fewer actions, almost ten a game! And Southampton has 58% of the possession compared to 42% of the possession for West Ham? The answer is simple: possession, or lack thereof, has little to nothing to do with tackles and interceptions.

If we were to apply Knutson’s formula to a comparison matrix between Mark Noble and Morgan Schneiderlin we would artificially inflate Schneiderlin’s tackles and interceptions numbers on the inverse basis of their possession % and artificially deflate Noble’s numbers on the assumption that he has more chances to tackle and intercept. The only problem is that here, between these two teams, that would be exactly wrong.

The problem is in the assumption. The assumption is that every time a team makes a pass it presents an opportunity to intercept. Similarly, that every time a player makes a dribble it presents an opportunity for a team to tackle. But not every team is trying to win the ball back with every opposition possession. Noble tackles less because his team tackles less. If you’ve seen them play you know that they are content with the opponents having the ball in their own half. Meanwhile, if you watch Southampton, they press. They try to force turnovers.

That’s just one example, there are others. In fact, Ted’s own regression analysis showed an R2 value of just .40. Only 40% of the variation can be explained by the model. That leaves a whopping 60% unexplained. I’ve done a fair number of regression analyses and I would probably never publish a .40 much less make some of the sweeping statements that Ted makes.

The thing about stats and especially football stats is that you have to keep them grounded in context: in the context of a team’s playing style, in the context of a player’s abilities and history, in the context of a league, the context of that league’s overall competition, and in the context of a league’s refereeing style.

I do think Ted is on to something. The idea that playing style matters to the end stats is bang on and you do see me taking into account a player’s contributions to the team’s whole. That said, possession only measures pass dominance. So, if I were to adjust anything for possession it would be passes. If I wanted to adjust defensive stats between two players, I might do something similar to what I have done above and compare those two teams’ tackles+interceptions ratios. Or even better, find out what the team’s tackle-interception ratios are in the League and then adjust for that.

But possession? I’m not even sure I like the possession stat as a “possession” stat much less as something I would use to adjust defensive output.

Qq

 

64-wilshere-agame-gt

Welcome Debuchy but what about Jenkinson? And if Arsenal buy a Khedira what about Wilshere?

Not much special going on today so let’s talk a bit about transfers.

Debuchy’s signing was announced yesterday and this is fantastic news because that marks Arsenal down as having bought 2 of the 5 positions that they need filled this summer. The best part is that we have made two major signings and we haven’t yet played our first pre-season friendly.

There was some speculation earlier that perhaps Arsenal didn’t need to buy a right back after Sagna left and the Debuchy signing put that to rest. Debuchy is a 28 year old French International with 18 months of experience in the Premier League starting every weekend. I think it’s also symbolic that Wenger bought the French player who kept Sagna from starting during this World Cup. This may be unpopular because Sagna was a fan favorite but Debuchy is an upgrade on Sagna.

Debuchy is younger than Sagna and he’s a more balanced player. When I compared Debuchy to Sagna and Aurier, the difference is stark: Aurier played as an attacking wing back at Toulouse, Sagna kind of didn’t do either defense or offense and instead was more of a passing outlet, and Debuchy was smack in the middle of the two.

Particularly impressive were Debuchy’s defensive stats for Newcastle. Comparing him against his own team’s percentages he made 17% of Newcastle’s tackles, 12% of their interceptions and 10% of their fouls.

Sagna wasn’t horrible but rather Debuchy was just very active defensively. Debuchy also can fill in for Sagna in the aerial duels department: Sagna has long been an outlet for Szczesny and Debuchy will hopefully continue in that role, he did after all win 4/5.7 headers per game at Newcastle.

 

I know that many people thought (hoped?) Jenkinson would get the starting job and some people went so far to suggest that Jenkinson and Bellerin could do the job but I think this signing puts that idea to bed and tucks it under Jenkinson’s Arsenal bedsheets. Wenger left the door open to Jenkinson saying that he can compete for the spot and further that he hasn’t made his mind up about who will be starting but that said I see this as another transition year for Jenkinson.

The crucial pairing, and probably deciding factor, will be right back and right forward. Jenkinson and Walcott do not seem to get along well in that regard. My observations are that Jenkinson tends to park far too forward and expect Walcott to cover for him. Walcott, being a striker, naturally doesn’t like this. The two of them publicly fought on the field several times with Walcott telling Jenks to stay back and Jenkinson shining Walcott on.

That issue is only going to be exacerbated with the signing of Sanchez who is an outright striker and will not cotton to having to run all the way back to defend for Jenkinson. And I have no problem with this, we didn’t buy Sanchez for £30m to play right back, we bought Sanchez to do the minimum defense up front (pressing and harassing) and to win us games with goals.

Sanchez’ strengths at Barcelona were that he took almost all of his shots inside the opposition box, which is what led to his outstanding conversion rate. You want a striker with a 30% conversion rate? He needs to play deep in the opposition area. For Sanchez to be an efficient goal scorer we need him to have the freedom to get in the opposition 18 yard box and cause havoc. He can’t do that while defending in our final third so that the fullback can whip in crosses to no one.

One other oddity that Wenger mentioned in the interview about signing Sanchez is that Sanchez could play in any of the positions up top, including through the middle and “with Giroud in a 4-4-2″. Now, I don’t know if Wenger is messing us or not and I struggle to think who he might play on the wings (Ox, Podolski, Cazorla, Rosicky? Özil would be wasted out there) but there might be a clue in there as to why Wenger is looking at Khedira. During Wenger’s most successful era he played with two in base of the midfield: Parlor and Vieira, Petit and Vieira and it was Gilberto and Vieira. That’s why Khedira and Ramsey is a mouthwatering prospect in midfield but it leaves so many questions: where to put Özil, and probably most worryingly, where does Wilshere fit into all this?

Wilshere’s stock has fallen off a bit (and I am not at all talking about his smoking) with even some of the most famous Arsenal personalities starting to wonder about his development. At this point in his career I’m more of the mind that he suffered a bit from his injury and frankly he suffered in light of the hugely successful season Aaron Ramsey had.

But the fact remains that he can’t take Özil’s place as the creative midfielder, he doesn’t seem to have the engine to take Ramsey’s place in midfield, and he’s not a defensive midfielder (at least not that he has shown so far). He’s also not a wing player, a forward, or a defender. So, if Arsenal splash the big cash on a player like Khedira or Bender where does Wilshere fit?

With Jenkinson on the bench? And how long will he be happy doing that?

Qq