Around football right now, we seem to be hearing that Arsenal are basically the same as every other year, but all the clubs around them have improved. Our numbers suggest that's not the case, and Arsenal's performance on both sides of the ball has fallen off this season.
Let's start with the obvious ones, the expected goals numbers.
Attacking xG 15-16: 1.97
Attacking xG 16-17: 1.67
Defensive xG 15-16: .95
Defensive xG 16-17: 1.09
So the attack is generating .30 xG fewer per game, while the defense is allowing .14 xG more. Combine the two and you get -.44 in expected goal difference, which is a huge whack when it comes to performance in the league table.
Where's that coming from? Well shot generation is down a touch on the attacking side, 14.6 to 15, but open play shot quality has fallen from .135 to .115 per shot, so the drop in attacking output is almost all down to the quality of shots Arsenal are generating this season.
On the defensive side of the ball, Arsenal are actually giving up FEWER shots per game - 10.64 this season vs 11.82 last year. Again, the reason for the swing in xG Conceded is down to shot quality. In 15-16, Arsenal's average open play shot against was worth .075 xG. This season? .105.
Arsenal's opponents are generating forty percent better shots than they were last season! What happened to all the long range pot shots?
In previous seasons Arsenal have gamed xG by generating 40-50% more shots than their opponents while having a huge quality differential between the shots they take and the ones they concede. This year the quality difference is almost completely gone, which has dramatically affected their expected goals numbers at both ends of the pitch. This feels like a strategic change on the part of their opponents, but maybe I'm reading too much into it.
How Do You Fix It?
This is a massive question and one that I don't really know the answer to. Are Arsenal defending badly? Have teams solved their defense, and because of that know how to create better chances against them?
Arsenal's attack is probably the best from a personnel perspective that it has been in ages, and yet that isn't exactly firing on all cylinders. Would Cazorla's presence magically heal all wounds? He only played 15 90's last year and the Gunners were much better then, so I'm not sure his absence again this year has enough explanatory power.
Average shot quality in attack is still better than the 14-15 season, but this has always been Wenger's special sauce that he brings to teams. This year it's still good, but it's no longer among the elite, and it needs to be for them to have a shot at winning the league. This year, it's just barely good enough to give them a shot at finishing 4th. This is also true because despite generating plenty of set piece chances, Arsenal are dead average in number of goals scored from them at 9.
Most worrying has to be the change in the defensive numbers. Arsenal tend to play a more passive style of defense than most of the top teams, trading shot suppression for forcing the opposition to take worse shots. However, this year they are giving up far higher xG shots, but doing it at nearly the same rate as before and basically at league average numbers. That's not gaming xG, that's just losing more games.
The question of why this is happening has lots of moving parts that seem to add up to a big problem. Monreal is finally showing a bit of age, and is no longer the elite defender he once was. though talented, Mustafi has had some issues bedding into the Premier League. Gabriel perhaps isn't as good as Arsenal thought when they bought him, and he's been forced to play right back when Bellerin is out.
Meanwhile in midfield, the aforementioned Cazorla may never be fully fit again. It's like Defensive Midfielder Groundhog Day Part 2, except instead of starring Mikel Arteta and his hair, we now have a different diminutive Spaniard playing the lead. Welsh hero Aaron Ramsey has played about the same amount as Santi, leaving Wenger to choose the so-called Dumb and Dumber axis of Coquelin-Xhaka as a double pivot, while occasionally adding El Neny, Oxlade-Chamberlain, or Alex Iwobi into the mix.
Last year's Arsenal looked like the best team in the league in the numbers, and a club that was close to taking the next steps in regularly competing for league titles instead of fourth place. This year's Arsenal looks almost exactly like their league position - likely to miss out on the Champions League for the first time in ages.
At least we know who to complain about all of this to. Unlike almost every other club in the Premier League, Arsene Wenger has full control at Arsenal. The question is whether he understands what the causes of the problems are, and whether he's adaptable enough at age 67 to rebuild this team for future title runs.
Despite a generation of good years together, Arsenal fans no longer seem convinced he's capable of anything other than 4th place trophies and Champions League knockout rounds, but they've certainly started yearning for something different.