Scatter graphics: Premier League, 15 Jan 2017
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).
This graphic’s in a pretty odd shape at the moment. In the top left you have three teams – Burnley, Sunderland and Hull – who are all allowing a lot more shots than anyone else (over 18 per match) and taking relatively few in return.
Next there’s a stripe of clubs across the equator from Middlesbrough to Palace who all allow a relatively similar (and average) number of shots and muster differing volumes, from worryingly below average to average, in return.
Lastly we have the dominant clubs in the bottom right quadrant, with Liverpool narrowly edging Tottenham as the side with the healthiest balance of chances. Spurs create slightly more while the Reds are less permissive defensively, with Chelsea and the two Manchester clubs not far behind.
Arsenal aren’t quite in the same league so far, with the balance of chances in their games more similar to Southampton than their fellow members of the top six.
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:
Arsenal and Southampton may take a very similar number of shots, but what happens next could hardly be more different. The Gunners are the division’s most clinical finishers so far, needing fewer than seven attempts on average to score each goal (which is how they’re keeping pace with the more dominant teams around them). Meanwhile the Saints have been the top flight’s most wasteful side in front of goal, with over 16 shots taken for each goal scored: more than twice what Arsenal have needed and around five more than any other Premier League side.
Man Utd and West Ham have both suffered similarly, albeit to a lesser extent, struggling to convert their above average number of chances created into goals.
In the bottom left it looks like West Brom owe their place in the top half of the table to some clinical finishing, having taken the third fewest shots in the division so far.
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:
There are three teams across the top who are all soaking up far more chances for each goal conceded than anyone else. Tottenham have been doing so in addition to allowing opponents few opportunities in the first place, Middlesbrough have faced an average amount and Burnley have permitted the most of any side, but all three defences are performing heroics.
Despite allowing even fewer attempts at their goal than Spurs, both Liverpool and Man City are among the three most porous defences in the top flight. Opponents aren’t getting many opportunities to score against them, but those that have been carved out have found the net with worrying regularity.
Leakier than both of those two has been Swansea, who might not be in such a dire situation if they’d been able to soak up a few more 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:
Interestingly when we adjust for shot quality, Chelsea have looked far more capable in defence than attack. No side has restricted opponents’ chances more effectively but the five clubs immediately beneath them in the league table are seemingly creating noticeably better chances on average.
In attack Liverpool lead the way with around two goals’ worth of chances being created per match, while at the other extreme Middlesbrough have only been averaging around 0.8 goals’ worth per game.
We can also see that while Arsenal and Southampton take a similar number of shots, the Gunners’ have been of a noticeably higher quality. However the difference is around 0.3 goals per match (1.7 vs. 1.4), so doesn’t come close to accounting for the whopping difference of 29 goals between their two tallies so far this season (which equates to 1.4 goals per match).
Swansea‘s leaky defence is less of a mystery here. Only three clubs – those we singled out on the first graphic – have allowed chances of higher aggregate quality so far this season.