Scatter graphics: League 2, 2020-21
Now that the season is over (barring play-offs which I exclude for consistency), I can create final versions of 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).
Carlisle were the most shot-happy team in the division by some distance and allowed fewer shots than anyone else, yet somehow only finished 10th. Cambridge and Bolton secured automatic promotion despite not dominating matches – at least not in shot terms. Oldham games were great entertainment for the neutral, with plenty of chances at both ends of the pitch.
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:
Here’s part of Carlisle‘s problem: only a few teams were more wasteful in front of goal. Southend‘s woeful finishing was a big factor in their relegation, while some ruthless chance conversion from Cambridge surely helped their promotion challenge.
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:
Salford‘s resilient defence almost bagged them a play-off spot – they soaked up more than twice as many shots for each goal conceded than bottom side Grimsby. In the previous chart we saw that Stevenage‘s chance conversion was among the worst in the division, but at least they made life difficult for their opponents too.
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, Cheltenham appear to be worthy champions, while Mansfield appear to have underachieved massively. Given that they finished 11th, it’s a surprise to see Leyton Orient among the poorer performers here.