Arsenal have the best defense in the League right now and Chelsea have the second worst defense in the League. I’m measuring that strictly by goals allowed: Arsenal have allowed 7 goals, Chelsea 17. But if we look a bit deeper into the numbers we see that Arsenal’s superior defensive record can be attributed largely to one man, Petr Cech.
If you watched the match against Manchester United on Sunday you saw Arsenal jump out to a 3-0 lead in the first 20 minutes. United has been insanely efficient this season and up to that match they had scored 70% of their Big Chances. Because I’m going to get asked in the comments I’ll just explain that Big Chances are easily illustrated by the two shots that Petr Cech saved in that match, one from Schweinstiger and one from Martial, both shots were right on the penalty spot. Another example is the backheel that Alexis scored, and the two open shots on the right, one by Ramsey (missed) and the other by Ox (hit the crossbar).
You can argue that “Big Chances’ is subjective (or even “too subjective”) but I think it’s got value as a stat since most of us see those chances occur and we sort of instinctively know that it was a dangerous shot. I also want to give credit to Opta, this is an official Opta stat, because I think they do a pretty good job of collecting this data for us. It’s rare that I disagree with them over whether a shot was a big chance or not.
Another metric that I use to judge whether a team is creating dangerous shots is the notion that there is a “Prime Area” from which team’s score most of their goals. This is a metric which preceded the expected goals craze and which actually helped to inform that work. Basically, if you look at the very big data (not individual games) you see a clear pattern develop where teams tend to score most of their goals, and have a very high conversion rate, from an area right in front of goal. This is the “Prime Area”:
Again, this isn’t unique or even very insightful. If you’ve ever played football you know that shots in and around the penalty spot and 6 yard box are the most dangerous shots to create and concede.
Prime Area shots and Big Chances often overlap and back to my earlier example of the match between Arsenal and Man U, the match which Arsenal won 3-0, if we look at Manchester United’s shot chart we can see that they basically created just two shots which were really dangerous. Both were Prime Area shots and both were Big Chances.
In fact, apart from those two shots, United were forced to take all of their remaining shots from distance, where teams score a tiny percentage of their shots (2-3%).
All of this is a long and boring way of explaining some of my definitions.
Ok, with that under our belts we can ask some questions! For example, I know that the top four teams (in terms of spend, not in terms of League position, because Chelsea are in…. uhh… scrolling… scrolling… 16th place) convert on average 36% of their Big Chances this season. This is the first season that I’ve collected this stat in detail so I don’t know whether that is high or low. Shots in Prime (or SiP!) are scored at a slightly lower rate of 22% among those same teams. Remember, I’m not counting Own Goals here, just intentional shots and goals scored off of those shots.
As we saw against Man U, Petr Cech smothered both of United’s Big Chances./SiP but that wasn’t a one-off performance for the Czech Republic keeper. He’s been stellar in front of goal all season and except that error for the first goal against West Ham, has been the best ‘keeper in the League in terms of saves from those dangerous areas like Big Chances and Shots in Prime.
In fact, Cech has saved 75% of the Big Chances he’s faced and 78% of the Shots in Prime he’s faced. Those other top teams aren’t even close to Cech’s numbers:
|Club||BC saves %||SiP Save|
Now, I will caution that some of these numbers are small. All four of those teams have only conceded a total of 46 Big Chances and 100 SiP. So, Cech’s numbers here are 6/8 Big Chances saved and his SiP save is 7/9.
If Chelsea had a keeper saving at the same rate that Cech is saving, they would have conceded 6 fewer goals this season. That must hurt Jose to know that he sold the best keeper to the best team in London and that that keeper is performing at a high level while the keeper he bought to replace him is performing at the level we expect to see from a 16th place team. That must sting like the tears of a clown, when there’s no one around.
This doesn’t mean that Cech will continue saving at that rate, I really don’t know what he’ll finish the season with, but it does mean that since the opening day howler against West Ham Cech has pulled off some great saves and given Arsenal’s lack of finishing up front it’s fair to say that Cech’s saves have probably kept Arsenal in the title race.
P.S. I have a lot more data from these Big Chances and SiP to share which prove that Arsenal are legit title contenders. I will dole that out over the international break.