Grantland's Mike L. Goodman wrote an interesting piece about the 3-man backline, using ManU & LvG as the prime example. But to contrast it, he also looks at the back three as employed by Pep Guardiola and Roberto Martinez. The LvG stuff is both ManU-centric and throughly covered elsewhere. The Guardiola system is also covered extensively. But Martinez...not as much.
Pep Guardiola’s back three operated completely differently from LvG’s. During his last season at Barcelona, Guardiola often experimented with a back three, often featuring full-back Dani Alves. And, in one of the odder football comparisons of all time, that’s similar to how Roberto Martínez operated at Wigan, before he moved to Everton. He used a handful of players you’d traditionally think of as full-backs or wingers as part of a three-man defensive line. Guys like Emmerson Boyce, Maynor Figueroa, and even Jean Beausejour started, nominally, as center backs. On the surface, this seemed insane.
The reasoning behind it, however, was and is surprisingly sound. Possession football, especially in the last several years, is predicated in part on having full-backs join the attack. As the full-backs push up the field, the two center backs split extremely wide and a midfielder drops between them. (Think Steven Gerrard, right before that moment.) In effect, many possession teams were morphing into a three-back squad anyway when they had the ball, but that three was made up of a midfielder flanked by two center backs, a formation known by its more traditional name, “three guys being forced to play out of position.” A back three comprised of at least one (and sometimes two) full-backs solves that problem. The wide defensive areas are patrolled by speedier full-backs, and a traditional center back sits in the middle.
It’s not hard to imagine Guardiola implementing a similar system with left back David Alaba as part of a back three at Bayern Munich. If you run that system, you better have the ball all the damn time, because you simply won’t have the physicality to deal with defending deep in your own territory otherwise. That’s part of why Wigan struggled so much defensively under Martínez. They were one of the only bottom-half teams to consistently control possession, but when they lost the ball, they conceded quickly and often. It made for entertaining soccer and won them an unexpected FA Cup, but ultimately the magic ran out.
Martínez has yet to break out the formula with Everton, but the team has a host of attacking wing talent now, and a couple of good young hybrid defenders like John Stones and Muhamed Besic (who played in the midfield for his country, Bosnia and Herzegovina, but featured at both center back and right back for his club in Hungary). Everton eventually playing a back three wouldn’t be at all surprising.