Monthly Archives: June 2015

An introduction to clearance maps

When I was busily logging all of those defensive stats to try and do something with individual defensive statistics (which will come first, a breakthrough in that or the next Game of Thrones book, eh, eh, amirite?) I started to come to the conclusion that, while clearances weren’t a great measure of defensive ability, they were a decent measure of the pressure a team has been put under.

After I stopped doing CB stats and started getting stats cravings again, I turned to clearances. From observation, I think they can be useful.

Sweden England U21s

Largely, I think you can divide clearances into 2/3 groups. The first is basically just the penalty area, or Red Zone. The second is a kind of trapezium shaped second box, or Orange Zone. This is a trapezium instead of a straight rectangle because at each side of it is a fairly non-essential area that full-backs occupy. These clearances generally, in my mind, aren’t too important, and don’t happen too often anyway.

This clearance map is for the Sweden U21-England U21 match. Reading it, it looks to have been an even match, both have similar numbers of clearances in total, in the Red Zone, and in the Orange Zone. Perhaps England put Sweden under slightly more pressure, as there seem to be a higher concentration of clearances in Sweden’s Red Zone, and England’s clearances give the impression of a higher line than Sweden, which suggests that the balance of play was pushed into Sweden’s half.

I didn’t watch the match, nor look at possession or shot stats before writing the above. England did indeed outshoot Sweden 14-10, getting more shots in dangerous areas too. They also had 58% of possession, which slightly surprises me, given how similar the clearance map looks. Perhaps England largely had control of the match, but failed to make it count in really forcing the matter, pushing Sweden back and creating chances, choosing instead to keep the ball and pass it around perhaps somewhat aimlessly (I can say this, I’m English).

So basically, that’s how you read a clearance map. Despite trying to push them, I’m still a bit hesitant about them. For one thing, I’m not sure how much I am reading into them what I want to read into them. I may not have known much about the U21 game, but I did know from the score that it was probably a close game with England edging it, which is what I read. Red Zone clearances will also be affected by corners, which could, in some cases, skew how the clearance map looks. Clearance maps will also work less well with Continental teams than English club sides, as they clear the ball far less. For example, season long clearance maps for the 2014/15 season champions from the La Liga and the EPL:

Barca 14-15 just BarcaMan City 14-15 just City

Below the heatmaps are rough Red Zone, Orange Zone, and ‘5th line’ totals. The 5th line total, in the EPL, is a rough proxy for how high the defensive line is. Man City is actually a bad example of this, because it very unusually goes down in total from column 4 to 5, then back up again at 6, which might suggest a brand of ‘charge and hope’ CB defending. For reference, in the Premier League, RZ totals are on average 550, OZ totals vary a fair bit, but usually between 200-300, and 5th line total EPL average is around 110. City are obviously a fair way below all of these.

However, Barcelona are HUGELY below these EPL totals, particularly the Orange Zone and 5th line, which are virtually non-existent. So perhaps, for now, keep a bit of distance from La Liga clearance maps.

Thanks for reading. Below is some more clearance map stuff that is less public-aimed, more stats-y.

I haven’t done too much correlational stuff yet, as I need to collect averages of everything and put it all together, but I have done it for one season, the Premier League 14/15. Total clearances per game had a -0.59 correlation with point totals, and ‘Red Zone’ clearances per game a -0.67 correlation. This is probably similar to why the Red Zone totals for Barcelona were much more comparable with the Premier League clearance maps than Orange Zone and 5th line totals. It also makes some sense. No matter how much you might want to pass the ball out of the back, there will always come a point (in your own box) where you’ve just got to boot it out of play and away from danger.

What next? Do more data-y stuff, to see whether Red Zone clearances are a good link to points totals elsewhere. Look more at clearance maps for other leagues outside of the EPL, to see if/how they can be of worth. Try and decide what clearance maps are actually *for*.

Can they explain why things happen, why teams win or lose, and thus how they can improve? It seems unlikely. They look like they can be used to tell the story of a match, or a general look at a team’s season, but is there any call for that?

Anyway, as usual you can comment below or get me on Twitter @ETNAR_uk

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Giving Clearances a Shot

The 3rd match on the 13th of February of the Premier League (or the closest date to the 13th that matches were played).

The above is the first thing I wrote of this article. For a while I’ve thought that the amount of clearances that teams make in matches, and places where they make them, can be used to tell the story of the match, in a similar way to shots.

Both, on the surface, have obvious flaws. You can shoot from anywhere and it’ll boost your shot numbers, and you don’t know how good these shots actually were. Similarly with clearances, many clearances might show good defending* or it might show opposition pressure or both, it might be hard to tell which is which.

I picked a random match to try and use clearances to tell the story because I figured this would help reduce a level of confirmation bias. If I’m picking the match myself, I’ll probably end up choosing one that shows how useful clearances are.

Anyway, the match in question turned out to be Chelsea vs Everton (1-0, from the 11th of February). I do not remember it (I see now that Matic was WhoScored’s man of the match, maybe this has something to do with it).

I go to look at the possession. Chelsea had 58%, Everton 42%, so Chelsea obviously dominated to a degree.

The shots back this up:

Chelsea vs Everton shots

Chelsea had 21 shots to Everton’s 7, with a good handful of Mourinho’s side’s being in the ‘danger zone’, central in the box.

You get something similar with the clearances:

Chelsea vs Everton clearances

Both show Chelsea as dominant. Clearances increases both sides’ in-box presence, although this may partly be due to defending corners, where clearances are likely to happen in dangerous looking areas of the box (although the same goes for shots, if you get on the end of it).

I’ve made some observations about clearances during my year or so looking at defensive stats. These aren’t backed up by thousands of matches of data, but I think they *generally* hold true.

Chelsea vs Everton clearances 2

Clearances made in the dark green area have a fairly good chance of having been headed clearances by defenders (from long, maybe hopeful, balls forwards), and I think the more dominant your team performance, the more likely they are to be headed (if you’re under pressure yourself then clearances in this area are more likely to be ‘genuine’ on the ground clearances, and you’re also more likely to be clearing away hopeful hoofs if your own team is dominating – these are guesses).

The yellow area are clearances that are bordering on irrelevant, having a higher likelihood of being made by wingers or full backs from throw-ins, for example. It is, therefore, somewhat intuitively, the red zone that is most important.Chelsea vs Everton clearances 3

So, if we’re to glance at the clearance map and tell the ‘story’ of the game, we can see that Everton had some presence in Chelsea’s box (1), but given the relative lack of clearances elsewhere (2) we can be suspicious of this and tentatively guess that corners had something to do with it (I checked, it did). Everton were also clearly bombarded (3) and the fact that a lot of their clearances were so deep (as shown by a rough, vertical line of best fit of their clearances, 4) shows just how pressed back they were.Chelsea vs Everton shots

Is there anything there that we couldn’t glean from looking at the shot map? Maybe not. We can see Everton had some presence in Chelsea’s box, but that most of their shots were from outside. We can also see that Chelsea dominated, and that Everton must have been pressed deeply back into their own territory.

So what does this mean for clearances? To be honest, I don’t know. The random match didn’t show anything great in support of taking more notice of clearances, but it also didn’t tear down the idea completely. It also gives a sense of where the team’s defence is in one handy map, almost like a defensive counterpart of the shots map, the other side of the coin.

(You can, of course, get maps of all of the team’s defensive actions, but they are generally more confusing, with tackles and interceptions across the pitch. I think clearance maps, like shot maps, are less messy and that comes with its pros and cons).

The use of the clearance maps in practical terms, probably, isn’t much. They might help you get an idea of how a game went if you missed it, but you can generally watch highlights, read a match report, or your Twitter timeline. It might give you a sense of whether a team was hanging on for a result, or just couldn’t break through to get one, but, as I’ve said, shot maps can give you this sense too.

Basically, this is an idea that’s been knocking around in my head and I thought I’d have a small bit of a closer look and report my findings, whatever they turned out to be. Of course, neither shot nor clearance maps are a substitute for watching the match analytically yourself, nor do I think clearance maps will really change how people think about the game. This is more of a tossing of the clearance hat into the ring and pointing to it, saying “Hey, what about this?”

 

*(For the record though, in my previous work with defensive stats, I’ve come to the conclusion that clearances aren’t a measure of good defending, at least on an individual level, even when possession adjusted, you’ve got to juggle defensive stats a lot more than that to get something worthwhile. Obviously match to match everything that stops an attack is good, but I believe clearances tell the story of opposition pressure more than individual or team defensive strength).