Scatter graphics: League 1, 2017/18
Now that the regular season is over, here’s a final batch of the scatter graphics, which 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).
Wigan have stood out all season as the most dominant team, so their return to the Championship isn’t much of a surprise. Peterborough are once again in the entertaining top right quadrant that they’ve made their own – they took almost as many shots as the Latics but allowed more than some relegated teams.
Plymouth may have narrowly missed out on the play-offs but for much of the season their underlying numbers looked dreadful, hence them being stuck among the relegated teams here. Bury meanwhile looked relatively decent in raw shot terms, but we’ll see below how it went wrong for them.
It’s interesting to see a huge gap between the nine teams on the left and the rest of the division on the right – without more data I’m not sure whether this is a tactical grouping between teams who look to out-create their opponents and those who prefer to play on the break.
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:
Bury‘s finishing played a huge part in their relegation: they may have taken comfortably more shots than the average team but they needed far more attempts than anyone else to find the net. Rochdale – who narrowly avoided the drop on the final day – look to have suffered from a less extreme version of the same problem.
Blackburn meanwhile were the division’s most clinical finishers, which helped them to keep pace with a Wigan team that created far more chances.
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:
Gillingham look to have relied heavily on their defence this season, allowing the most chances in the division and soaking up more for each goal conceded than anyone else. Three of this season’s play-off challengers – Scunthorpe, Plymouth and Peterborough – also look to have successfully absorbed lots of shots.
While Bury can blame their forwards’ poor finishing for their relegation, Oldham‘s problems look to have been in defence, where they repelled fewer shots for each goal conceded than anyone else.
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, three of the top four stand out, with Wigan again leading the way. Shrewsbury‘s brilliant season looks to have been a huge overachievement, although even in the data they’ve taken huge strides forward since last season.
It’s been a strong return to the division for Blackpool and Portsmouth, while Rochdale looked good enough to have avoided that last-gasp relegation escape altogether.