Guest post by Scott Willis
Yesterday, I had a series of tweets on Arsenal’s defense and Petr Cech that caused a bit of a backlash against me and had people questioning my sanity. I wanted to take some time and move from twitter to a medium that actually allowed for a bit longer and a more nuanced explanation of how I arrived at these conclusions.
My main point is that Arsenal’s defense is mediocre this season and that they are more closely resembling a team fighting for a Europa League spot instead of one that is fighting for a Champions League place.
I also made the point that I thought that Petr Cech was a big reason that the goals allowed stats suggested that Arsenal are still in the conversation for top 4 and that had people questioning my eye sight and if watched Arsenal play at all.
I will try to dig through these with a little more depth and longer explanations.
First is the argument that Arsenal’s defense Is mediocre this season.
I have created a database of fairly detailed shot stats this year and one of the things that I was playing around with this morning was creating a ratio that compared different stats as a percentage of league average. Using this method is popular in baseball as a quick way of seeing how far above or below someone is above average and I thought it would be interesting to see for the Premier League.
As I did this it became very obvious that Arsenal are very unlike the other five teams above them in the table defensively.
First is the percentage of shots allowed per game compared to league average for each team.
|TEAM||Percent of league average|
Chelsea are really good at not allowing teams to get any kind of shot off against them, the other top 4 contenders are not too far off but bringing up the rear is Arsenal. Arsenal are better than average but they are not nearly on the same level as the other teams they are chasing.
Next let’s look at shots in the danger zone. The danger zone is classified as the six yard box plus the center of the 18 yard box. This is where the vast majority if goals are scored and where you really want to limit shots taken from.
|TEAM||Percent of league average|
The story is the same for this measure, Chelsea are really good at limiting shots from the danger zone. The other top teams are fairly close (except Tottenham have dropped off a bit) and allow well below the average team leaving Arsenal better than average but not in the same league as the others.
Next let’s take a look at the shots allowed on target.
|TEAM||Percent of league average|
Perhaps I should just copy and paste what I wrote the last two times down here. There is Chelsea leading the way, there is a chasing pack and then a big separation and there is Arsenal.
Next let’s move to something that gives more context to the quality of shots allowed besides the location alone and look at big chances. Big chances are an Opta stat that says that the chance was one that you would be expected to score regularly (in my data set they are scored 47% of the time)
|TEAM||Percent of league average|
This time things are different but still look bad for Arsenal. This time it is Manchester United who allow the least big chances compared to league average, followed by City and Chelsea. Tottenham is above average but not great and Arsenal and Liverpool are just about at the league average mark. This last bit could go a ways in explaining some of Liverpool’s issues; they don’t give up many shots but when they do they are high quality chances.
Lastly let’s take a look at overall chance quality allowed (what I like to call my version of xG). Chance quality takes many things into consideration, where the shot was taken, was it with feet or head, how was it assisted, was it considered a big chance and puts it all together based on the historical weights each of these have on scoring chances.
|TEAM||Percent of league average|
Unsurprisingly after looking at the previous numbers Chelsea come out the leaders followed by the teams from Manchester and then Tottenham and Liverpool with Arsenal bringing up the rear with a number that suggests they have the 7th best defense in the league the same distance to Everton in 8th as Liverpool in 6th.
After looking at these numbers I think that I rightly concluded that Arsenal do not have a defense that normal title contenders have, let alone a defense that you would expect to be able to challenge for a top four spot with six other strong teams. That conclusion is further buttressed by watching the team on a regular basis where it has become apparent that there are some major structural issues with the way that Arsenal defend over the last couple of seasons.
That brings me to the second part of the series of tweets that seemed to have people questioning my sanity; Petr Cech is a large reason why the top line goals allowed numbers don’t look too bad. Arsenal have allowed 27 non-penalty goals this season which is 4th best. This is 8 goals behind Chelsea, Tottenham and Manchester United who are all at 19 but ahead of both Liverpool and Manchester City who have much better shot based stats than Arsenal.
Doing the same kind of analysis as before but using simply the non-penalty goals allowed as a percentage of league average you get the following table.
|TEAM||Percent of league average|
Arsenal are right in the thick of things now with the 4th best mark. Chelsea still lead the way tied with Tottenham and Manchester United. Manchester City is in 5th well behind what the other stats suggest and bringing up the rear in Liverpool. For all of these teams you can construct a solid narrative about their position on the table compared to their stats based on their goal keeper.
Chelsea have a solid defense and the numbers are improved by having Thibaut Courtois in goal. Tottenham have good stats but that is elevated into an elite defense at prevent goals by Hugo Lloris. Manchester United have adapted to Jose Mourinho’s defensive minded ways and have a good defensive unit that is again elevated David de Gea in goal. Manchester City have good defensive numbers but these have been undermined by the goalkeeping errors of Claudio Bravo and the same can be written of Liverpool and their rotating duo of Loris Karius and Simon Mignolet.
I essentially did the same thing with Arsenal, I saw that they had pretty mediocre stats yet the overall numbers looked fairly decent and came to the conclusion that Petr Cech is actually a positive influence on Arsenal’s overall defensive numbers.
I do want to defend that a bit more but first I want to illustrate some limitations in the data I have above. That does not include penalties, normally I don’t include penalties in when I am looking at offensive stats because that is a different skill than when you are looking at scoring but that is a major thing that you want a goal keeper to be good at stopping. Cech has faced 7 penalties this season and stopped none of them while looking like he had no chance on almost all of them and that should be held against him. The second part is that goalkeeping stats are very crude, it is hard to assign credit/blame to a goalkeeper compared to his defense. It is also hard to examine things without knowing where a shot was placed and knowing things like his positioning.
All of those caveats out the way the numbers do suggest that Cech that while he is no longer among the elite he is still a good shot stopper as long as the shot isn’t a penalty. Arsenal (and with Cech playing the vast majority of the minutes) have the 3rd best save percentage behind Tottenham and Burnley. Arsenal also have the 5th best expected goal efficiency which could hint at a good goal keeper helping to keep more goals out than expected.
All of that said, I too can see that Cech is on the downside of his career and that it looks like he has taken a step back this season. I would be happy to see a new keeper come into Arsenal next season to take his place but if that does happen I would warn against putting too high of expectations that it will fix things without a change to the defense in front of the goalkeeper.
Scott Willis tweets at Oh That Crab
Of course Arsenal’s poor defending and defensive skills are not Wenger’s fault because nothing is ever Wenger’s fault..
Sounds pretty bitter from someone calling themselves Happy Days
STRAW MAN ALERT
Thanks for the article Scott. I noticed one weird thing about Cech. He seems pretty good at stopping one on one shots but if someone shoots from 15 to 20 yards out, he hesitates.
Yeah, maybe it is that weird way people remember things but it does seem like he does well against hard shots but lets in more soft ones than expected.
He had a real problem with saves from 18+ yards last season but that’s improved this season.
Neat stuff, Scott. I admit I’m having a hard time wrapping my head around your percentages though. I take it if Arsenal are at 93%, that means they are 7% better than the league, on average, at that particular thing. This is a bit confusing because it’s a comparison used to illustrate another comparison. Why do you choose to present your data that way? This is simple stuff, you could just give totals +/- standard deviations. Then, a paired t-test can give you an idea of statistical significance. Percents are misleading because they give no sense of the size of the data or the randomness of the distribution. Ok, I’ll get off my nerd box now.
Having said that, I can’t argue with your conclusions, though I will say it’s apparent simply from the goals against column that we have a problem. Also, some people on Twitter need to find a new hobby.
I am not sure most people would have as easy a time following standard deviations, people seem to have a hard time understanding basic statistics let alone describing distributions.
I used percentages because I got the inspiration from baseball statistics which often uses this format.
Just think if you’re going to do stats, might as well go whole hog. Then you can present your findings in layman’s terms. I think most people intuitively understand what it means to be a standard deviation above or below the norm.
“The numbers do suggest that Cech that while he is no longer among the elite he is still a good shot stopper.”
That’s the problem! Cech in his prime was a world-class goalkeeper, now he’s level with many Premier League keepers. Cech is still better than a Valdes, Boruc or Bravo, but he’s below the level of a Courtois or De Gea. Even a goalie like Heaton is having a better season than Cech.
Also keep in mind that Cech has been responsible for a couple penalties this season. His slow legs are a weakness. While Ospina is very good in 50-50 challenges, Cech is often late to the ball.
And last, while Cech has improved on long-range strikes, he hasn’t done a great job on some of the goals he has conceded this season. The obvious example is Sterling’s winner in the City game. Cech was beaten at his near post with a low shot and had a better chance of making a save with his leg than with a diving effort.
Should szczesny be back as no 1, considering his performance at Roma?Else who is there better than Dave and Pete,who we can realistically get?
Enjoyed this but I don’t think Cech’s shots allowed stat up us anywhere near a conversation about top four.
The other percentages are too damning and we are running out of time with just 11 games left. And we still have Man City, Man United, Tottenham, Stoke and Everton to play. Even with a game in hand on most of the teams above us, 2 in the case of Liverpool, this is as an uphill a battle as we’ve ever had in recent times in a team populated by a bunch of surrender monkeys (Alexis excepted).
I am hoping that staying out of Europe altogether might help us better rebuild the team around a focus on domestic competition.
What bafles me is whether this kind of statistics is available for the authorities before the season starts
It’s so reliable and trustworthy
The problem is all about the defense
Heh. “The authorities” really made me laugh. Makes it seem like there’s some kind of structure at the club.
So Liverpool wins. Arsenal will not overtake a single team above them in the table. I’m pulling out my map of Europe to do a refresher on Slovenia, Macedonia, Belarus etc. That’s where we’re playing our European football next season.
You can add the ” the players were tired from the trip to Ukraine on Thursday ” to the already long list of excuses used by Arsene next season, but my favorite are still the automotive related ones:
“Playing with the handbrake on” and “stuck in the second gear”.
Makes you wonder what kinda driver Arsene Wenger is.
Tom, I think those are descriptions, not excuses. An excuse is defined as an “attempt to lessen the blame attaching to (a fault or offense); seek to defend or justify.” Playing with the handbrake on is a way to describe the way the players played, not an attempt to lessen blame or justify the play. It’s admitting that the players were not at their best. It’s a classic Wengerism, which, I’m gathering, is what you’re really sick of. But I do think you’ll miss those one day.
Claudeivan, NK Maribor hails from Slovenia and they were in European competition, including the CL, not long ago. Macedonia’s best team is FK Vardar, who have never qualified for the CL. The pride of many in Belarus is BATE Borisov, who were in the CL not once but twice, for the first time in 09-10. At any rate, where we play is a lot less important than how we play.
Hey doc, you are of course right about the difference between excuses and descriptions but I disagree that it doesn’t matter where we play next season.
There are still many sub-standard pitches , at least in comparison to what Arsenal players have been used to, and going to some of the more obscure clubs in Europe in January or February, especially those in colder climates, will not be an experience Arsenal players will have cherished.
Personally, I think Wenger should throw the remainder of the season once it’s obvious Arsenal can’t make top four.
Let Everton and West Bro take the Europa spots, especially the West Bro fans deserve going into Europe to show off their manager’s tactical brilliance on the bigger, internarnational stage.
Great thing about Arsenal throwing a game or two, no one would have even the slightest suspicion, because most Arsenal players look like they’ve been doing it most of the season 🙂
Can’t be much worse than the lower league pitches we play on in England. Besides, we’ve been to choice locales almost annually anyway: Greece, Ukraine, Bulgaria, etc.
I do find it ironic how willing people are to throw games after spending so much time berating players for lack of fight/effort/passhun all season. To me, that never works. Even if you are trying to win next year, the foundation for that has to be set this year. You can’t just show up in August and expect it to be different.
Relax doc. I was just kidding.
Wenger would never throw a game. Not intentionally anyways.
He’s done it many times though, by not giving his players the tools to win on the day.
Besides, even with no Euro commitment next season Arsenal’s chances for the PL title would be very low.
Tom, I know Wenger would never throw a game, but from your comment it didn’t sound like much of a joke that you thought we should throw games. After that, you’re not helping your case by talking about how low our chances will be next season. Really? Why should we be so bad? I mean, isn’t this our best squad since the Invincibles (I’m not sold that it is, but it’s close)? And what does low mean? On an earlier post I guesstimated that in this closely contested league with lots of more or less evenly matched teams, our chances of a title are close to 10% season. That’s pretty low, but it’s probably better than it’s been in years. The odds are not greatly in our favor. However, it’s gambler’s fallacy (the worst, most obvious form of bias) to assume our chances next year will be affected by our form now or the outcomes of previous campaigns. Yes, Wenger’s singular and outdated management style does have a certain familiar feeling, but in football what matters most is 1) the availability of difference making talent 2) the sustained fitness of key individuals and 3) key moments in big games. The identity and style of the manager is a distant 4th behind those factors, in my view, though Wenger’s role looms larger as the horse and pony show around his future continues to roar on unabated.
Of course it was a joke.
Strategizing on behalf of one’s club is predicated on caring for said club and I stopped doing that a while back , sadly.
Arsenal will most likely continue to struggle next season for variety of reasons.
Alexis will be gone, Thursday Europa games will be a shock to the players’ system. Klopp and Guardiola will be another TW closer to what they envisage to be their ideal line up.
Look, I picked Arsenal to finish third this season.
I didn’t think all new top tier managers would finish ahead of Wenger in their first full season at their new clubs.
I was wrong, I admit it and I’m not making excuses for myself.
You’ll get there eventually,. Everyone at their own pace I suppose.
The salt rub in the gaping wound of general Gooner angst is now, thanks to Big Sam’s side suddenly playing real football, the ugly prospect of S%&rs within shouting distance of Chel$ki. Ouch! And if Chel$ki’s form starts to wobble with some tough games ahead (Man City, Man Utd, etc), it could get really ugly.
Regarding Cech….and for that matter, issues with every keeper we have had for several years…..maybe Cech is not actually in decline, but perhaps, just perhaps the coaching for keepers at Arsenal is substandard.
David seaman tweeted that arsenal lost their best keeper coach when Tony Roberts went to Swansea…..and was never replaced, leaving goalkeeping legend…..Gerry Peyton as GK coach, as he has been since Bob Wilson retired.
Wenger refuses to shift backroom staff, no matter how they perform. Gerry Peyton. Openly criticised by
Szcz, at pains to tell the world how he enjoyed working under Jens when he did his badges, he played pretty well too, Fabianski, Seaman and then recent articles by Cech praising his old Chelsea coach, Lollichon.
Gerry Peyton…..anyone see a problem here…..even if that world renowned guru of goal keeping, Arsene Wenger does not?
Still, Wenger has his values that he has imposed on the club, loyalty to the underperforming high amongst them…..values..and that’s what count….right?
Well, that didn’t take long.
Five minutes to go but win, lose or draw, much, much better stuff from us today.
As always, it’s the hope that kills you
Positive: Didn’t lose.
Negative: Spurs might win the title.
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