Kepa troubles: Analysis of how bad goalkeeping & bad luck is costing Chelsea

Frank Lampard raised a few eyebrows with his decision to drop £72 million goalkeeper Kepa Arrizabalaga to the bench for their match against Leicester before their winter break but statistics highlight why the Blues boss is right to feel frustrated.

Chelsea have conceded 34 goals this season, almost ten more than their expected goals against (xGA) figure of 24.3 according to FBref.

The graph above tracks each team in the top ten’s cumulative game-by-game performance against expectation by subtracting the actual number of goals conceded in a match from their xGA in that game.

Chelsea are comfortably the biggest underachievers in the top ten (and 19th out of 20 overall) with their graph featuring a pretty sustained downward trend as the Blues consistently conceded more goals than the quality of chances they gave up. The only continuous period when it moves upward coincides with their six-game winning run from weeks seven to 12 of the season.

The Blues have allowed just 76 shots on target (second only to Liverpool’s total of 70 heading into this weekend), but the 34 goals they have conceded is 19 more than the runaway leaders and only two fewer than Newcastle, who have faced almost double the amount of shots on target (141).

Part of the discrepancy can be explained by bad luck and randomness with opponents’ finishing prowess, but Kepa continues to look a weak link.

He has the second-lowest save percentage of all keepers to have played 19 or more games in the past decade, and comes out bottom of all this season’s regular stoppers based on the Post-Shot xG metric on FBref, which judges keepers based on the quality and direction of shots they face once they are registered as hitting the target.

A crumb of comfort for Chelsea is that it’s possible to expect them to benefit from a small positive regression towards the mean.

Kepa’s numbers last season were a bit closer to league average, so if he (or Willy Caballero) can produce a marginal increase in performance from current low level, even to something just below average, it would represent an improvement that would bolster their hopes of maintaining a top-four spot.

It’s also reasonable to hope that teams won’t have their shooting boots on quite so often against them in the future.

While Chelsea have let in five goals from the last eight shots they’ve faced on target, Monday's opponents Manchester United have failed to find the net with their most recent 16 attempts on target, showing how a team’s luck can blow hot and cold.

Lampard will hope things start to turn his side's way, regardless of who he selects between the sticks.

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