Chelsea have underperformed xG in the past 2.5 seasons

Chelsea’s offensive weaknesses under Thomas Tuchel are coming under increasing scrutiny, although the new head coach remains undefeated with six wins in nine games in charge. But while Chelsea have only conceded two goals in that span, a truly impressive number, we’ve only scored ten goals, which is also pretty impressive, and not in a good way.

Or maybe not, if we’ve been paying attention to it for a few years.

Frank Lampard had lamented Chelsea’s inability to complete their chances throughout their 18-month tenure (even when the team were losing goals at near-record rates), and before that, Maurizio Sarri’s Chelsea depended heavily on Eden Hazard to ward off something from nothing. And while Hazard has had just about a better career season as a farewell gift, Chelsea have consistently underperformed expected goals, like this pretty Chart by data analyst Mark Taylor shows.

Taylor compares the 15 Premier League teams still present since the start of the 2018-19 season by illustrating the difference (using a 10-game moving average) between the goal differential and the expected goal differential, in effect showing the quality of the finish of a given team. was relative to the (expected) mean. Blue is good, yellow is bad.

You need a magnifying glass to see the blue on the Chelsea chart.

Most of the top performing teams in this metric should come as no surprise. XG’s outperformance is the hallmark of “good” teams, after all.

Liverpool have consistently outperformed average on the way to a few historic seasons and a long overdue Premier League title. Manchester City have also outperformed, albeit a little less spectacularly, showing how they continue to be a well-oiled machine. Kane & Son & Co-powered Spurs are also up there, even after Pochettino, while Manchester United have had a bit of a roller coaster ride.

On the other hand, on the side of the “bad” teams, we find Chelsea. Maybe no other team has underperformed as consistently as we have. Brighton is approaching. Wolves stagnated a long time ago. Southampton and Everton experienced a few massive crashes but found their way back into the blue. Even Burnley has had notable periods of recovery from the average. But not Chelsea, except for a few tips of good finishing form.

Photo by Catherine Ivill / Getty Images

Of course, xG is not the purpose of soccer statistics, and it’s just another metric by which we can look back and gauge a team’s success. But it is what we are and have seen on the ground. It doesn’t reveal anything new, but it puts it in an obvious and visible form. We weren’t as good at converting odds as we were at creating them – which, if you consider that we made more moves than any team but one last season, explains some of our problems during that time.

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(Obviously creating lots of half chances can rack up xG sums similar to a few big chances, but that’s a breakdown beyond the scope of this quick glance. But it’s certainly worth noting that if Chelsea created the second most ‘chances’ / shots in the league, we were only in the middle of the table in terms of shot conversion metrics.)

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So what is the solution?

Sarri asked Hazard to bail him out. Lampard sacrificed the defensive structure for more creative luck. Tuchel did essentially the opposite. They have all sought the mythical balance in the meantime, and have found none … yet. Can Tuchel do it in the middle of a season? That’s unlikely, which would explain why he’s apparently aiming for a top-four finish – and defense-first approaches can pay huge dividends in Cup and knockout competitions as well.

The long-term solution can be a little more complicated than that and require tactical and personnel changes. But maybe that’s a goal for another day.