Analytics: Chelsea’s early season struggles

The Premier League champions have begun their title defence with a bit of a whimper picking up only four points out of a possible nine.

Outside of the matches themselves Chelsea have also attracted some negative headlines with off-field issues from Joe Mourinho’s public disagreement with the club’s first-team doctor to the ongoing John Stones transfer saga. All in all it has not been a good first three weeks for Chelsea.

The plus side for the Blues is that it has only been three games and there are still lots of matches to be played. However some of the trends that have emerged from these opening matches are more than slightly concerning.

First, it is important to note that although Chelsea ran away with the league title last season many of the more advanced statistics told a different story.

Chelsea’s Total Shots Ratio (TSR)—the ratio of shots a team takes relative to the number of shots they both take and concede—of 0.58 was only the fourth best in the league behind Manchester City, Arsenal and Liverpool. Chelsea’s slightly inferior TSR suggests they weren’t quite as dominant as their eight-point lead at the top of the table last season showed.

Another advanced statistic that can give us a better insight into a team’s underlying performance level is Expected Goals (ExpG). ExpG calculate the probability that any given shot will be converted into a goal while taking into account factors such as distance to the goal, angle to the goal, speed of attack and part of the body. For example if a shot has a 30 percent chance of being scored it is worth 0.3 ExpG.

Chelsea had the highest ExpG difference in the league last season with +31.4, only slightly higher than Manchester City’s of +31.0. This tells us that while Chelsea may have appeared to be the run-away team in the Premier League last season, the numbers indicate they really weren’t that far away from their competitors.

Given that the sample size to go off of the current campaign is so small, it is important to keep these numbers in mind when looking at how Chelsea have progressed—or failed to progress—in their opening three matches.

Chelsea’s first match of the season was a 2-2 draw against Swansea City in which they were quite lucky to escape with a point after Thibaut Courtois was sent off. Swansea had 1.7 ExpG to Chelsea’s 0.7, which becomes 2.3 ExpG to Chelsea’s 0.7 if we include Swansea’s penalty shot. All in all it was a very poor opening match of the season for Chelsea.

The one major bright spot for Chelsea over these opening few weeks has been the surprise signing of Pedro, who impressed on his debut versus West Brom providing a goal and an assist.

It’s hard to predict what Pedro will bring to this Chelsea side, the main reason being that it is very difficult to look at any ex-Barcelona player’s numbers and disentangle them from the “team effect” of playing for Barcelona. It’s much easier to put up great numbers playing alongside the best team in the world than it is anywhere else.

In his final season with Barcelona Pedro played 1531 minutes, and averaged 0.4 goals and 2.2 shots per 90 minutes. He also averaged 0.4 assists and 1.5 key passes per 90 minutes. For a Barcelona player these aren’t stand-out numbers by any means, but then again it is very difficult to stand out at Barcelona.

However, looking at assists and goals together Pedro was able to provide 0.8 goals and assists per 90 minutes. If he is able to replicate these numbers at Chelsea that would certainly make him a successful signing.

So what does all this mean for the defending Premier League champions? They’ve had their difficulties to start the season and despite their final table position last year they probably weren’t eight points better than the rest of the competition. However, they’ve added a solid attacking player in Pedro and are still in pursuit of another major defensive addition in the shape of John Stones.

Over the next few weeks we should get a better insight into whether these signings will help turn around the team’s fortunes.


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