Scatter graphics: League 2, 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).
Bury remain the most dominant sides in the division, with league leaders Lincoln occupying a far more modest area of the graphic. Quality trumping quantity is at least a partial explanation here, as the rest of the charts will show us. MK Dons are the undisputed entertainers of the division, with an average of almost 27 shots in their matches this season. Despite sitting in the mid-table, Grimsby and Stevenage have done far more defending than attacking this season.
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:
Cambridge and Lincoln are polar opposites here: the Imps lead the division despite creating relatively few chances because they’re absolutely ruthless at converting the ones they do carve out. Cambridge meanwhile have one of the most productive attacks in the division but their finishing has been woeful: they’ve needed more than twice as many attempts on average to put the ball in the net. Port Vale have also struggled to turn a relatively respectable number of opportunities into goals.
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:
Mansfield and MK Dons have both got their stubborn defences to thank for sustaining their promotion campaigns, while Grimsby have gotten away with allowing the most shots in the division by far due to their tenacity at keeping the ball out of their net. Bottom side Notts County haven’t allowed opponents a ridiculous number of opportunities but they’ve been the worst by far when it comes to repelling shots.
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 well as I’m able to measure it – then Grimsby stand out as the worst-performing side, so I’m not sure how they’re sitting so comfortably in mid-table. It could be that their poor start is skewing the numbers, but if things stay the same then I’d expect them to drop a bit before the end of the season. Bury look to be the strongest side overall, although MK Dons, Mansfield and Lincoln aren’t far behind overall – the Imps are far more impressive at the back than up front, while the opposite is true of Paul Tisdale’s side.