xG Check, 4 Feb: Tottenham & Mourinho try to kill Expected Goals
With some people just not willing to accept Expected Goals (xG) as a metric that can be used meaningfully, it's crazy, unlikely results like this that leave xG disciples having to defend the method.
There are a few opportunities here that are overrated by most xG models, particularly Raheem Sterling's (0.51 xG) blocked shot - Toby Alderweireld is standing directly in front of him - but Sergio Aguero's poke wide from 18 inches right on half-time is, if anything, underrated at 0.62 xG. Add in Ilkay Gundogan's missed penalty (0.75 xG), the blast over the crossbar by the same player while stretching (0.56 xG) in the second half - and that's before we even get to the culmination of lower xG efforts peppered all around the area.
Given Steven Bergwijn's body position and mass of defenders in front of him, his goal is just 0.07 xG, with Son's clincher higher at 0.3 xG - and even then this is aided by a huge deflection from Fernandinho.
But xG fans, fear not; this is, quite literally, the type of match that is the exception proving the rule.
In a bizarre day, on average we should have seen four goals at Turf Moor but instead we got nothing. Jay Rodriguez's (0.6 xG) smash against the crossbar was the clear miss of the match and should probably be given a higher total, while Jeff Hendrick's free header (0.54 xG), completely untouched by the defender, should have found the corner.
At the other end, Alexandre Lacazette and Pierre-Emerick Aubameyang were responsible for the large percentage of Arsenal's misses, but Auba's effort, running clean through with no-one near him only to skew miles wide of the target, was a better chance than xG has credited. All in all, a game that should never have finished goalless.
This was a strange game, one where two big incidents swung the perceived xG in Norwich's favour. Lukas Rupp was awarded a gigantic 0.75 xG for a first-half chance that didn't even make the highlights show - he wasn't even facing in the correct direction and his tame back-heel was easily blocked - a clear example of context needing to be applied.
Likewise, at the other end. Joelinton's header was parried by Tim Krul but Miguel Almiron's follow-up header is unchallenged and just six yards out. Headers are generally given a lower xG because, on average, they are scored less. But the position of Almiron, running onto the ball with very little in his way, he really should score higher than the 0.4 xG granted to him.
So in effect, this match was on the margins, with not much between the sides and certainly not the chasm that xG suggested.
What is xG check?
Each week FC will aggregate the Expected Goals (xG) ratings from three respected sources and provide an average for both the home and away team. From there we will assess which matches have ended in a different manner than the xG would suggest.
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
But sometimes, xG doesn't tell the whole picture, so we also analyse the highlights of these games to look at the chances created by teams in a little more detail.