Expected Goals are a useful metric over the longer term, because any good xG model will see its players regress back to the mean over time. It means that are certain points of a season we can assess a player's goal total, compare it to their xG total, and identify players who are either over or underachieving the model.
EXPECTED GOALS (xG) assesses the quality of a shot based on several variables such as assist type, shot angle and distance from goal, whether it was a headed shot and whether it was defined as a big chance. From there that shot is assigned an xG score and the cumulative total of these scores provides a team's xG for a match.Stats Definition
See the tables below and be sure to click the related article for more reading from James Tippett's box entitled the Expected Goals Philosophy.
This data gathered from the Understat model, which can be found here.
Vardy's efficiency for Leicester for this season has been phenomenal and it's no surprise that in the past month as Vardy's goals regressed back to his xG (his over-performance had been much higher than this) so too have Leicester hit an overdue return to average.
Danny Ings, meanwhile, is getting more confident in front of goal as he continued to convert. He has had more shots in his past three matches than he managed in his previous 10, and though that's not always a good thing - confident players often shoot from more difficult positions - he's most definitely on a hot streak at the moment.
Aubameyang, meanwhile, while still overachieving, has his number tied up predominantly in away games at Watford and Norwich, where he struck four goals from just five shots, total.
There's one player that confounds Expected Goals metrics each and every season, and he's the only one to do so. Step forward, Lionel Messi.
His masterclass this season involves scoring four direct free-kicks carrying a combined total of 0.26 xG which already sends him miles ahead of the curve. It's easy to overestimate how likely a goal is to be scored from a certain position or the player who is hitting it, but for example in the 5-2 win over Mallorca in December, Messi's three combined goals totalled 0.24 xG. Put simply, Messi breaks xG rules because he is Messi. The model works - Messi doesn't operate in our universe.
Phillip Max's score can be largely explained by his three free-kick goals from ludicrous distances - one of which carried an xG of just 0.02 - so Jadon Sancho's performance is much more interesting. Sancho has taken just one shot inside the six-yard area - predictably scored - while the rest are from improbable angles, generally as he drifts inside from the wing.
Serdar's figure suggests that he will struggle to maintain his decent run in a Schalke team that has needed his input.
Ciro Immobile's numbers are, in the main, superb. Scoring 7/8 penalties already puts him 1.75 ahead of xG, while two goals from improbable positions away at Bologna added a huge additional 1.85 xG. In short, he is over-performing largely because of these incidents and, in the main, his positioning and overall goal-to-xG record on a match-to-match basis is good.
Underneath, Andreas Cornelius, Domenico Berardi and Christian Kouame are ahead of their modest numbers.
It will be a cause for concern for Lyon that the quality of chances that they are created aren't good enough, and it has required the skills of (the now-injured) Memphis Depay and (maybe up for sale?) Moussa Dembele to score some of the goals they have. There's a reliance on the rest of the team now to produce better chances - OL are six ahead of their team xG total.