Since Thomas Tuchel’s arrival, Chelsea has almost exclusively used some version of three at the back. The formation has a lot of advantages in its ability to create (temporary) overloads anywhere on the pitch and then fall back into a solid shape if need be. It also suits a Chelsea side that still has a bit of Antonio Conte in them from years ago.
But many fans have clamored for a return to a back four for several reasons. First of all, it adds another midfielder or attacker and Chelsea is not short on either. That leaves one less defender, but defenders have few fans when things are going well. Furthermore, Chelsea’s attack has suffered at times while the defense has been amazing, so the thought might be that the Blues can afford to cut loose and be more adventurous.
The problem of switching to a back four comes with the back four itself. Chelsea’s struggled defensively with four at the back and combinations matter. It’s not as simple as picking one defender to take out of the side and then everything works. This is a finely tuned machine we’re talking about here.
At the heart of any defense is the centerbacks. In a back three, those wider centerbacks are expected to create passing opportunities and even venture forward into the midfield with the ball. The centermost one often stays deeper just in case, sweeping up anything that breaks through.
With a back four, there is much less affordance for players in the mold of those wider centerbacks. Fans will well remember all the times David Luiz would venture forward, leaving his partner all alone for a counter. Instead, the defenders in a back four need to be more like that centermost defender in the back three. They need to be able to read the game and be somewhat more passive as others take charge. At the same time, however, you don’t want both of the defenders being too similar. You want variety on your team in many ways within a certain bounds.
That’s where Chelsea will struggle most with a switch to back four, should it come. Antonio Rudiger has been great under Tuchel, but he’s also been able to venture forward and take advantage of a spare man behind him. Cesar Azpilicueta won’t be in the running for a centerback pair. Andreas Christensen and Thiago Silva would make a lot of sense on paper given their current roles, but Christensen has struggled in a back four previously and Silva’s age is going to make the shape harder for him over time. Trevoh Chalobah could be an answer with either of those two, but a formation switch that banks on a young player, even if they have been fantastic, seems to be a risky decision.
The fullbacks are also another important consideration. While there is much less that separates a fullback and a wingback than many like to admit, the main difference is in their range of actions and the time they have. A fullback will have more time in possession to work with the ball with their team, but less off it to get back into position. They can still press like wingbacks do, but Chelsea fans already saw under Frank Lampard how quickly the two centerbacks can get outnumbered on a counter.
Ben Chilwell and Reece James will be the future of wingback or fullback but as fullbacks they’ll be expected to come in more often as well as stretch the play as needed. As wingbacks they are really only tasked with the latter. It won’t be a massive shift for either but it is a consideration when discussing Azpilicueta and Marcos Alonso. Both absolutely can perform the role of a fullback, but their speed will be a detriment at times in a position where speed matters.
But the issues of slower fullbacks or defenders needing a certain amount of cover can be solved with the right midfield and press. The press more than anything is important because it will play the biggest part in the selection of the deepest midfielder (also the player most akin to the third centerback). With the right net ahead of him, Jorginho can excel in this role. Other Jorginho, however, the options dwindle down to basically just Chalobah. Now, Chalobah could again be a risky choice but here he could at least replicate Marquinhos’ role at Paris Saint-Germain for Thomas Tuchel, shuttling from midfield to defense and 4-3-3 to 3-4-3 as the game needed. If Chelsea is to go to a back four at some point, further reinforcements here are still a priority.
After that, the rest of the midfield shape matters. Tuchel could opt for a “dual 10” system not unlike the one Lampard used, but it seems unlike that he breaks away completely from the idea of a pivot. Plus, Chelsea already presses in a 3-1 shape up top most of the time so a 4-2-3-1 makes the most since overall. The main difference for the pivot will be working more in tandem with the fullbacks and wingers. Instead of being completely static, they’ll need to be comfortable rotating in and out of channels at times. That would arguably be the biggest adjustment for a 4-2-3-1.
The remaining decisions are largely straightforward as they aren’t too different than what Chelsea already does. The right variety in the front four will be important (and something Chelsea’s failed to do a few times this season) but their ability to press will also be crucial to providing the safety net the rest of the team will need. Most of the forwards were brought in with those ideas already in place but even the ones that don’t press often or effectively should find some minutes with some of the weight taken off their shoulders.
Four at the back is certainly doable, but it will come down to finding the right combination of players that can support and cover for one another. It’s not as easy as simply dropping one centerback for one midfielder or attacker. Plus, three at the back still very much works overall at the moment, even if sometimes it is a bit labored and it leaves some important players out. Four at the back can be a trump card for later but it will be one that requires lots of preparation and planning.