Unai Emery made his name at Valencia and Sevilla using a 4231 system. Indeed, when Pep Guardiola was asked about Emery before the season on Sky, his last word was, somewhat jokingly, “4231.” It was the system Emery used against Manchester City, and then Chelsea, and then every Premier League game, Fulham aside (where he used 4222), until Bournemouth. With Arsenal facing a tough run of fixtures—a good Bournemouth away, Tottenham at home, Manchester United away—in the space of ten days, and having drawn their last three in the league, Emery did something surprising: he ditched the back four, which features both shapes that he likes to press in, for a back three, a system he has used for every league game since. While Emery has switched to a back four against Spurs and Huddersfield, the switches have been a combination of tactical and due to injury, and have come after relatively solid defensive performances. Indeed, almost paradoxically, as Arsenal’s centre back options have dwindled, the use of the back three has become to make more sense.
Yet that is not surprising. Recent switches to back threes in the Premier League have come after periods of defensive instability. Under Antonio Conte, Chelsea switched to a back three when 3-0 down against Arsenal, having lost 2-0 to Liverpool the match before, and didn’t look back, going on to win the league. In the same season, Arsène Wenger, a back four man almost all of his life, switched to a back three with Arsenal having gone on a terrible run of away form—a prelude to the 2017/18 season—and recovered to beat Manchester City and Chelsea in the FA Cup, and miss out on the Champions League by a point.
Indeed, when Arsenal switched to a back three under Wenger, I wrote that, “Indeed, the attacking nature of the wingbacks is not different to how Arsenal usually play”, and that, “By playing the fullbacks as wingbacks, it gets the two higher up the pitch without losing so much defensively.” The use of fullbacks as attacking players under Emery is perhaps even more true than for Wenger. For Wenger, the fullbacks were crucial in building play. Rather than building through the centre, Wenger’s sides would look to use fullbacks to carry the ball forward to play into midfield, and then create overlaps. Emery wants his fullbacks to spread high and wide, to create the overlaps, as he wants his side to build play through the middle.
Eighteen months on, and the rationale for making the switch remains largely the same; indeed, perhaps more so, given that Laurent Koscielny is largely a question mark following his Achilles injury. The one downfall is that with three centre backs and two defensive midfielders—as opposed to Wenger’s midfield of Xhaka and Ramsey—the importance of an attacking midfielder is heightened, in order for Arsenal to move the ball in attack and utilize the wingbacks.
Yet using the back three does not have to be a reactive move, and indeed, does not even always utilize three central defenders. Arsenal’s back threes, under Wenger and Emery, have seen fullbacks deployed as central defenders. Wenger used Kolasinac and Monreal, Emery is likely to use Monreal, and Stephan Lichtsteiner started against Huddersfield and came on against Manchester United as Arsenal ran out of centre backs. Using a full back at centre back works in part because the demands are different in a back three than a centre back pairing. In a back three, the two wide centre backs are responsible for covering the space behind the wing backs; thus, being adept in one on one situations, having the nous and ability to stand attackers up, and having more pace than your average centre backs is all of paramount importance. So too is being on the ball; the wide centre backs have lots of passing options, between the central midfielders and the wingbacks, and can also drive into space, as Cesar Azpiliceuta did for Chelsea and Kyle Walker did for England during the World Cup.
Furthermore, in a back three there is more cover. Most teams utilize attacking full backs or wingbacks one way or the other, and on counter attacks, the space left behind by full backs is often the space that can be exploited, as defensive players look to cover that space and open other areas of the pitch. With a back three, there is one extra defensive player to cover that space, and to cover a defender if they commit to winning the ball. It also allows a more defensive full back to still be in the side, and an attacking full back to be utilized at wing back, which is why Monreal can play as a left-sided centre back with Kolasinac at left wing back, and why Bellerin would likely not find himself used as a centre back.
While Emery’s historical preference is for a back four, utilizing three centre backs can get him through two big challenges: Arsenal’s collective weakness at centre back, both in terms of quality and numbers. It may only be a temporary measure, but in a season dedicated at extracting as many points as possible to get back into the Champions League, it may also be a necessary measure, at least until Emery and Arsenal’s recruitment team have the ability to address the centre back position with longer-term solutions.