There is going to be a fair amount of expected goals (xG) chat in this piece. So for those not familiar with the performance metric, I'll leave it to former Chelsea head coach Thomas Tuchel to broadly explain.
"You can lose games in football by being unlucky and you can win games with luck and the result does very often not reflect what happened on the pitch," Tuchel said in an interview with Sky Sports last year. "So expected goals gives you a clear view: how many chances you allow, how many quality shots you allow. It's good to have that figure.
"As with every number, the more you look into it you can find your benchmarks. So we know how over a season or half a season what the level of Expected Goals is if you play in a certain structure. If this is suddenly higher we ask ourselves, 'What's happening within the structure?'
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"If we concede double the amount [of expected goals] we are tempted to say we're in a very unlucky streak at the moment because obviously, the quality [of the shots] that we are giving away is not enough to concede so much and still we concede. That's hard to take."
Tuchel's discussion about xG was framed around defensive solidity; perhaps no surprise if you watched his Chelsea side. Yet the metric can also measure – at least to some degree – attacking efficiency. Score more goals than expected and it is likely you possess high-quality attacking players. Score fewer and it is very possible you're a team coached by Graham Potter.
As highlighted by Get Goalside – a football analytics newsletter – the 47-year-old has been in a battle with the Premier League xG gods for three-and-a-half years. It started during his time in charge of Brighton and Hove Albion and has carried into his time at Chelsea, although the Blues' inability to take chances predates Potter.
During Potter's first campaign at the Amex – 2019/20 – Brighton finished 15th in the table and scored a modest 39 goals. Their xG for that season, per FBref, was 45.4. It was a noticeable underperformance but one that, as Tuchel outlined, could be put down to an unlucky streak.
Then came the following season – and what appeared an unlucky streak became a genuine issue. Potter's side finished 16th in the table and netted on 40 occasions. However, their xG for the campaign was a far more impressive 50.9. Only Fulham, who ended the campaign relegated, were more wasteful in front of goal.
A pattern was set. Brighton would play well, create chances, and not take them. Some felt all the Seagulls were missing was a top-level forward. Others questioned whether expected goals models overvalued the chances created by Potter's system.
Last term – which proved Potter's final full campaign at the Amex Stadium – Brighton claimed ninth spot. It was the club's highest-ever finish but the goals were still not free-flowing. They scored 42 times but still couldn't match their xG, which was 46.2.
Potter may have broken the curse this season at Brighton; the Seagulls were actually up on their xG in the six games he oversaw. But then he took charge at Stamford Bridge, and history has repeated itself.
In the 17 Premier League games overseen by Potter as Chelsea head coach, his side have scored a meagre 15 times. Given the resources available, that is simply not good enough. But those who have watched the matches in question will know very good chances have been spurned by a number of players.
The latest came against Southampton at the weekend. Raheem Sterling, who otherwise played well after being introduced from the substitutes' bench, missed two clear opportunities in the second period. And that is partly why, per FBRef, Chelsea are already underperforming their expected goals by 5.2 under Potter.
It is something that needs to change – and quickly given Chelsea's results. If not, then Potter may lose more than simply his battle with expected goals.
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