The truth about clean sheets
It’s often implied that the sign of a good defence is the number of clean sheets they keep. Yet it’s a stat heavily reliant on luck and one that doesn’t necessarily tell the whole story.
For example, a team could be peppered with shots throughout the match but due to poor finishing and goalkeeping exploits, they manage to keep the opposition out and they register a clean sheet. Another team could dominate for 90 minutes, have total control but see a deflected shot beat their man in goal. All their good work is undone and they don’t get a clean sheet, despite being fairly solid defensively.
Even over a sustained period of time, clean sheets aren’t always indicative of a solid defence.
Take Liverpool’s 2012/13 campaign. The Reds kept 16 clean sheets in their 38 Premier League outings, second only to Manchester City’s 18. Brendan Rodgers’ side managed to shut out the opposition in 42% of their matches. However, they still finished the season having conceded 43 goals. Working off averages per 90, they either kept a clean sheet or conceded twice.
Some parts of the media praised Liverpool’s defensive resilience while overlooking the fact they’d been breached 43 times in 22 matches. That is why clean sheets only make up part of the bigger picture.
Leeds United find themselves in a similar situation. Marcelo Bielsa’s men have kept six clean sheets in total – more than Liverpool, Manchester United and Leicester City. They rank joint-fourth for this particular metric with only Manchester City, Aston Villa and Southampton (all on eight) able to boast a better record.
However, the newly-promoted side rank 19th for expected goals conceded (xGC). Leeds are only one of two teams, along with West Brom, to have an xGC total over 30 – 33.37 to be exact.
At their current rate, Leeds are on course to keep 13 clean sheets but have an xGC total of 75. By comparison, Chelsea are also on target to keep 13 clean sheets, using their current averages, but would finish with an xGC total of 39. Looking at clean sheets only, Leeds and Chelsea are as good defensively as each other. But when the underlying numbers are assessed, there’s a significant difference of 36 goals.
The best defence in the Premier League this season belongs to Manchester City. Pep Guardiola’s side rank first for clean sheets with eight and their xGC is the lowest in the Premier League at just 13.93. They’re the only team in the English top-flight to have an xGC per 90 average of below one (0.93).
The defensive unit at the Etihad is getting extra attention this year for three reasons. Firstly, Leicester hit them for five at the Etihad. Secondly, the team aren’t scoring as many goals. Finally, they’re bedding in Ruben Dias, John Stones is back in the starting XI and Zach Steffen has been playing in goal recently. There’s been a lot of change in a key area of the team, yet City haven’t let their numbers slip.
The truth is, the Citizens have, statistically, had the best defence in the league for the past four seasons. No team has kept as many clean sheets (64) and they’re the only team to have been in the Premier League for all four of those seasons to have an xGC total below 100.
Clean sheets are the opening chapter in the ‘How good are you defensively?’ book. If you’re genuinely interested, nobody just reads the first chapter.
All the graphics and visualisations in this article use Wyscout data and were produced in the Twenty3 Toolbox.
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