Confidence - an xG viewpoint

In the early months of the season Huddersfield were massively under-performing and the xg stats suggested that their form would increase dramatically and it did with 7 points taken in November but since then both actual and expected performance have dropped significantly and I think a possible explanation is confidence - that being below our xg totals for so long has actually made the squad believe in themselves less and thus produce less quality chances so our xg output sunk and thus are actual goals scored stayed low instead of rising up to the xg average. So I wanted to look and see if it is a common occurrence for clubs xg to move to meet ag rather than the other way round which is to the best of my knowledge what you would expect for a team under or over performing their expected goal scoring ability

Take a look at 5 game rolling expected goals (xg) and actual goals (ag) for both Southampton and Huddersfield this season:


Southampton
as - 5 game rolling average actual goals scored
xs - 5 game rolling average expected goals scored
Huddersfield Town



Both teams start the season severely under-performing in their actual goal scoring rates vs their expected scoring rates. But as the season goes on both teams pick up and start to score more goals and get back to the expected values. The difference is in what comes next, for Southampton they have slowly been creating less goals all season and once the actual goals catch up to expected they start to follow the decreasing pattern too.

For Huddersfield on the other hand the actual goals decrease rapidly again while xg maintain and even increase in the short term,  what you would expect to see after that are Town's ag rising again to meet xg but instead the xg actual starts to fall to meet the static average of ag and then ag decreases again before xg follows. This is behaviour described above, xg moves to meet ag, which I think can be put down to a team's confidence and how it can affect xg output.

My idea is that the Huddersfield team was clearly expecting to maintain their actual goal output of weeks 11-16 as that's the rate of goal scoring merited by the chances they create and when they in fact didn't over game weeks 17-21, they assumed that the weeks of increase were an outlier/extreme and not in fact what they had deserved - there was no way they could be under performing for this long and in fact the chances they create must only be good enough for 0.5 goals per game. This in turn then causes their actual chance creation to decrease as the team believes they aren't creating good chances so they stop and thus xg falls to meet ag.

I feel this is a pretty good explanation for the shape of Huddersfield's graph and their big problem this season and the Southampton example shows that even if xg is trending downward actual goal output should jump up to meet it which Town's doesn't so suggests there is something else at play. There may be better examples of this out there, I just chose to focus on Huddersfield first as they are my club. Coming soon a look into some other examples from this season and last.

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