• June 7, 2022
• Olaoluwa Nwobodo

Chelsea sold Kurt Zouma to West Ham United for £29M at the beginning of last season. He had fallen out of favor after the arrival of Thomas Tuchel at Chelsea. In the process, they sold an important component that made them strong in offensive set pieces. Tuchel opted to go with Cezar Azpilicueta, Thiago Silva, and Antonio Rudiger as his centerback partnership and never really looked like changing it. Zouma still made league appearances in the league under Tuchel, but most of his minutes were moved to cup competitions. This meant that Zouma had a decision to make. Tuchel expressed a willingness to let Zouma leave if Zouma indicated that he wanted to go.

Zouma had made the most appearances at centerback in the Premier League for Chelsea in the last two seasons he was at the club. From the start of the 2019/20 season to the end of the 2020/21 season, Zouma made 52 appearances as a centerback, making 47 starts. In that time, Christensen made 38 appearances, Rudiger made 39 appearances and Azpilicueta made 18 appearances at centerback.

Tuchel was well within his rights to decide that he did not need Zouma anymore, however, with Zouma Chelsea had more than just a superb centerback; they had a bonafide set-piece threat. Letting go of Zouma meant that Chelsea should have been aware that they were crippling themselves in offensive set pieces, and should have prioritized replacing that threat.

It seems Chelsea was not fully aware of what they were losing when they agreed to the deal with West Ham.

Chelsea was significantly less threatening in set-pieces last season in the absence of Kurt Zouma, especially compared to their rivals Liverpool and Manchester City. Comparing Chelsea’s season with Zouma and their season without him reveals a glaring difference in terms of set pieces. Note that “set-pieces” in this piece include corners and indirect free-kicks but not direct free-kicks. Looking at corners alone, in the 2019/20 season, Chelsea took 247 corners and generated 103 shots from them, totaling 9.7 expected goals (xG) in 38 games. Liverpool took 259 corners, generated 86 shots, and gathered an xG of 7.83. Manchester City took 297 corners in the same season and generated 103 shots as well, but gathered an xG 9.15.

In set pieces altogether, Chelsea gathered 11.83 xG, Liverpool gathered 10.94 xG and Manchester City gathered 13.57 xG. Admittedly, Chelsea took more shots from those situations, but that’s part of the point, as Chelsea took fewer set-pieces than those teams.

The average xG of a shot from a corner for all teams came to roughly 0.09, however you may notice that Chelsea generated more shots from fewer corners. This means that Chelsea gathered more xG from corners than Manchester City and Liverpool despite taking fewer corners than them. This was Zouma’s first season back from loan at Everton. Chelsea converted 42% of their corners to shots, compared to 33% for Liverpool and 31% for Manchester City.

Zouma’s impact on set pieces was more pronounced in the 2020/21 season. Chelsea took 121 shots from set-pieces in that season, generating an xG of 15.16. This was more than Manchester City and Liverpool, who took 107 shots (8.85 xG) and 117 shots (10.97 xG) respectively. Note that in this season too, Chelsea took fewer corners than both clubs, and it stands to reason that Chelsea would’ve taken fewer free kicks too. Chelsea also averaged 0.13 xG per set-piece shot, which was more than Liverpool (0.09) and Man City (0.08).

There’s more. In this season, Chelsea also converted more corners to shots, converting 42% of their corners compared to Liverpool (36%) and Man City (35%). So far, it has been established that when Zouma was in the side, even last season when his minutes significantly went down in the second half of the season, Chelsea was a better threat from set-pieces than Man City and Liverpool.

Then the 2021/22 season came along. Chelsea took five fewer shots from set-pieces (not much difference, eh), but they generated 6.59 xG less than the 2020/21 season. Yes, they took fewer shots, but five fewer shots do not account for 6.59 less xG, especially when you remember that the xG of a shot is always less than 1. Liverpool took 191 shots from those situations, City took 156 shots. Liverpool gathered an xG of 19.93, compared to City’s 20.47. Chelsea, compared to them generated 8.57 xG. Of course, more shots mean more xG, but the fact that Chelsea took 79 fewer shots than Liverpool from set-pieces and corners when they had been taking more than them in previous seasons is telling.

It gets worse. Chelsea averaged 0.07 xG per shot from these situations, compared to Liverpool’s 0.1 and Man City’s 0.13. Remember when that 0.13 used to be Chelsea? What’s the difference between the Chelsea of last season and the Chelsea of the two previous seasons before that? Zouma.

“Well, that doesn’t necessarily mean that it’s related to Zouma leaving!” No, but when you consider that Zouma has contested and won more aerial duels than Antonio Rudiger and Andreas Christensen in his last two years at Chelsea, you’d see why his presence in the side is helping Chelsea generate shots from corners. A player doesn’t necessarily have to be the one to take the shot in a set-piece situation. Their presence can benefit the team in other ways. They could draw players away from their teammates, making their teammates in better positions to take a shot from a corner.

Think about it. If Zouma and Thiago Silva stand in the box and the opposition team has just one player with the ability to match Zouma in the air, they’d put that player on Zouma, and this leaves Silva with a more favorable marker. In fact, Zouma scored the second-most goals for Chelsea in the 2020/21 season (5), despite barely playing in the second half of the season. Four of those five goals were headers from set pieces, and all five of them were from set pieces. Three of them were from corners. No centerback in the Premier League scored goals than Zouma last season.

Zouma’s aerial numbers aren’t the only proof that he was the difference in set pieces. West Ham United’s numbers in set pieces this season have been impressive, and Zouma played exactly the same amount of games for them this season as he did in his last season at Chelsea (24). West Ham took 97 shots from set pieces and gathered 11.1 xG, notice again that they generated more xG from set pieces than Chelsea with 19 fewer shots.

They also averaged 0.11 xG per shot from set pieces. Yes, Craig Dawson was a major part of their set piece threat, but when you have Dawson and Zouma to mark and you have to pick one, Zouma’s resume in the air doesn’t suggest you pick the other guy. West Ham’s average xG per shot did go down from 2020/21’s 0.12, however, they lost Angelo Ogbonna (1.9m) to injury and Issa Diop (1.95m) barely played. Zouma came in and their threat from set pieces remained potent because 0.11 xG per shot is quite strong as an xG per shot from set pieces.

West Ham has a much taller squad than Chelsea, which is why when Chelsea lost one of the few tall players they had, especially one who was as impactful in set pieces as Zouma, they shouldn’t have expected to continue with business as usual without replacing him.

All xG statistics are from UnderStat. Number of corners are gotten from SofaScore.