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Closing the gap
Arsenal gave Manchester City a good title fight this season, what is left to close the gap to them
Arsenal have led the Premier League pretty much all season, they looked like a strong team but still a step behind Manchester City. This is the big factor in that even with a lead on points, few Arsenal fans felt comfortable in this position. So in this post, I want to go through what underlying numbers are needed to challenge CIty and really get a sense of what Arsenal needs to do to close the gap and where the differences are between the teams.
The following is based on work by Ben Griffis at Cafe Tactiques where he took the concept of Pythagorean Expectation that was introduced first in baseball and adapted to other American sports to give an estimate of wins/points based off of runs/points/goals differential.
I am going to use the expected goals version primarily because I think that is a better forward-looking estimate but it would be ever so slightly better if you were to use goals instead.
Manchester City’s metrics of 77 xG and 31 xGA translates to 91.4 expected points over a full season pace and that should be roughly in line with what they finish the season with where they will be when the season ends.
Arsenal’s metrics of 69.1 xG and 41.5 xGA translates to 78.2 expected points over a full season pace and that puts Arsenal a bit above on actual points. They have quite the gap to close to get to numbers that would support a 90+ point pace.
I am starting to think of my targets for next season and I think this will help led the way on it, so I took the model and worked backwards to see about what sorts of xG for and against get Arsenal to the level required.
Improve the defense
If Arsenal look to improve the defense and want underlying numbers that would beat Manchester City they would need a big improvement. Holding the attack constant, the expected goals against would need to drop from 1.12 per match to 0.74. That number would be the best in the Premier League by a wide margin and would still be better than what the team saw during the best run of the season before the World Cup.
I think we would all like to see the defense improve but looking to see THAT much improvement from one season to the next might be asking too much.
Improve the attack
If we do the same holding the defense constant and looking to only improve in attack it again points to a pretty massive improvement needed.
Arsenal’s attack would need to go from the current 1.9 to 2.8. That is a level that again even at the best this season they did not hit for extended periods.
While this sounds like an incredibly fun team to watch, I am not certain that getting that level of improvement is realistic (that’s an 106-expected goal pace and would make Arsenal one of the best attacking sides of all time).
So rather than looking to just maximize one category to close the gap, the more realistic approach is trying to see combined improvement in both chance creation and suppression. After thinking about this I think a realistic target for defense is probably a bit better than what we saw with William Saliba in the team before the World Cup, with 0.9 per match. That’s an improvement over the full season but so much that it feels like an unrealistic stretch.
In attack, I find myself coming back to the Arteta quote “To be with the top teams this season you need to score 90 to 100 goals at least,” and think that he was on to something. This year it looks like Arsenal will fall just short but that should be the target and getting the underlying numbers to back it up will be key. To make the numbers work it pegs the per-match xG at 2.3, Arsenal have touched that this season but it is still a nearly 25% improvement on what they have done this year (it would also be better than Manchester City this season).
It is hard to look at this and think that is anything but optimistic, especially the expected goals but that is what it takes to close the gap (and get ahead) of what Manchester City have done.