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ANALYSIS: Which are the unluckiest teams in Serie A this season?
Despite this long-term correlation, teams will often over or under perform their expected goal difference within a season. An example of this is Swansea City in the Premier League last year, who finished 8th but had drastically overachieved given the chances they created over the campaign. This time around, they have faced a relegation battle.
In this sense, we can conceptualise ‘luck’ as how likely something would be to happen again. In footballing terms, expected goal over-performance is often driven by unsustainable finishing rates (above long-term trends) for you, as in your attack scoring more of its chances, or against you, as in your defence conceding less of its chances.
For the opening of this two-part look into which teams have been lucky in Serie A, we will be looking at teams who have under-achieved their expected goals difference.
We can measure this overachievement by calculating the difference between a team’s actual goal difference and its expected goal difference:
Over-Performance = (Actual Goal Difference) – (Expected Goal Difference)
If a team’s ‘over-performance’ is greater than 0, they have been ‘lucky’, and if it is less, they have been ‘unlucky’. Here, we will only look at teams for which it is negative.
Udinese, currently 17th in the league despite an expected goals difference that is the 10th best, have been the unluckiest team, closely followed by Verona and Lazio. Verona seem to have been really rather unfortunate – their expected goal difference is 15th in the league, yet they lie dead last at the moment, 12 points behind Frosinone.
Through separating attack and defence, we can see whether a team’s over-performance was driven by them scoring more or conceding less than the long-run trend.
Of Serie A’s under-achievers, Empoli are the only team whose attack has scored more than might be expected. It looks as if most of Udinese and Verona’s under-performance can be explained by their attacks being unlucky – Udinese’s attack creates the 9th most expected goals in the league, Verona’s the 11th, yet they are both currently tied for the least goals in the league with 26.
Atalanta’s defence are the only of the league’s underachievers to concede less goals than it should have, while Lazio’s has noticeably been the least lucky. According to my expected goals model, Lazio have the 3rd best defence in the league, yet they have conceded the 12th most goals. As a team, under-performing in a season isn’t necessarily a bad thing. If you can register where you have and not change things for the sake of it, you can limit the long-term effects of a short-term run of bad luck. For some, though, a downturn in luck can have dire consequences; had Verona’s attack finished the chances it created at a normal rate, they might not have been last in the league.
Bobby Gardiner @BobbyGardiner
