Scatter graphics: Premier League, 19 Mar 2019
I realised over the weekend that it’s been a fair while since I updated the scatter graphics. These compare the attacking and defensive performances of every team in a division. Each of the four graphics is explained briefly below and at length here.
First of all, here is how the number of shots taken by each club compares with those they face in return. The average number of shots taken per match is on the horizontal and the average number faced is on the vertical, so bottom right (take plenty, allow few in return) is good while top left (take few, allow plenty) is bad. The stripes are like contours: the greener the stripe, the better the performance (and vice versa for red).
In raw shot terms it’s the same story as before Christmas: Man City tend to dominate matches and currently take over 10 more shots than their opponents on average. Liverpool and Chelsea are the only sides anywhere near as dominant, while Burnley stand out as the team who spend the most time on the back foot.
Now let’s look at attacking alone. The horizontal axis stays the same as in the graphic above, but now the vertical shows the average number of shots needed to score each league goal. Therefore bottom right is good (taking lots of shots and needing fewer efforts to convert) and top left is bad:
It’s hard to say whether Huddersfield‘s season is more ruined than this graphic, but their eye-wateringly bad shot conversion is far from ideal either way. They’ve needed over twice as many attempts as the average team to score each league goal this season. Chelsea‘s desire to recruit another striker in January is understandable given their relatively average finishing this season despite having created all those chances – a clinical Arsenal side have scored more goals despite carving out far fewer opportunities.
Next let’s look at the defensive situation – basically take the above chart and replace the word “taken” for “faced” on both axes. Now top left is good – facing fewer shots and able to soak up more per goal conceded – and bottom right is bad:
Despite having sprung a few leaks lately, Liverpool‘s defence still looks excellent overall. If the last chart wasn’t bad enough for Huddersfield, they’re also leakier at the back than anyone except Fulham despite allowing their opponents a relatively respectable number of opportunities (fewer than Man Utd for example).
Finally here’s an attempt at correcting the first graphic for the quality of chances created and allowed, using the same “expected goals” values that power my shot timelines (explained here). The reason for doing this is that the results tend to correlate more strongly with performance than when we treat all shots equally:
When we adjust for shot quality (at least as accurately as I can measure it), Liverpool are a lot closer to Man City overall, with Chelsea a clear third. Man Utd‘s problems seem to have had more to do with their defence than their attack, but overall they look stronger than they did before. Crystal Palace narrowly lead a clutch of four sides who are the closest to the established ‘big six’.