Sheffield United might feature fairly low down a list of clubs believed to have influenced world football, but a cunning tactic they introduced in League One could be integral to their Premier League survival - and may well spawn copycats everywhere.

United's innovative use of 'overlapping centre-backs' has drawn praise from many, including master tactician Marcelo Bielsa, who said last season that, "Sheffield United's manager is someone with new ideas, I have seen very few people with these kinds of ideas."

But what are 'overlapping centre-backs'? And what's the point?

How it works

Sheffield United played a 3-4-1-2 formation in the Championship and League One, and assistant manager Alan Knill says they identified a need to create overloads against opposition teams who sat deep and blocked space.

The solution, born on the training ground, was to have the wide centre-backs sprint forward and overlap the wing-backs, and though Chris Wilder has taken the plaudits for this unique tactic, Knill is credited with creating it: "I wouldn't say one person came up with it," he told Telegraph Sport when asked.

As the centre-back overlaps the wing-back tucks inside, creating a two vs one situation against the opposition full-back, which frees up space for the centre-back to cross towards the strikers and drags defending players out of position.

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Sending centre-backs into the opposition half sounds risky and, in theory, could leave the team vulnerable to counter-attacks - this is something Sheffield United have worked on.

"We tend not to [send both centre-backs forward at the same time]," Knill explains. When one goes the other stays... in the past we’ve had both up and one crossing to the other!

"We actually find it drives the opposition back. Their forward tends to track the run and that forces them deeper - if you continue to do it, they have to."

Additionally, because one of the two central midfielders must cover the space by dropping closer to the remaining centre-backs, Sheffield United's deepest lying players - and therefore those with the most space and time on the ball - are their best at distributing passes, with Oliver Norwood key to how Chris Wilder's team plays.

It looks great in action. Jack O'Connell is the overlapping defender in this example from a win over Derby last season

O'Connell runs to overlap on the left

O'Connell is able to stride forward unmarked since teams rarely bother tracking opposition defenders - nobody expects the overlapping centre-back - and moves towards the wide space.

O'Connell wins space to cross

With United's left-sided centre-back now the left winger, O'Connell can cross the ball towards two specialist strikers in the box, with the '10' supporting in space behind, supported by the wing-backs.

In this example, O'Connell's cross finds Billy Sharp in the area, who heads past the Derby goalkeeper to score.

Sharp scores a header

"We need to have possession of the ball to allow our system to work and fortunately we have the personnel," Knill explains. "We’re lucky we have Chris Basham, who’s a midfielder, a centre-half, and a wing-back - he can play anywhere.

"Jack O’Connell was different because he's a left-sided centre-back and it took time to encourage him to do it, but we thought that would improve his game and make him more attractive to bigger clubs. We need the right players but the problem is that finding another Basham is difficult."

Not every centre-back has the necessary attributes to execute the run and operate on the wing - it's unlikely we see any lung-bursting runs from Phil Jagielka any time this season, for example - but expect Basham and O'Connell venturing forwards far more at Bramall Lane than in away games.

Why Sheffield United started using it

The difficulty with attempting this move in the Premier League is that United won't have as much of the ball as they did in the Championship and will simply have fewer opportunities to attempt it. Knill says that despite the quality of opposition, Sheffield United want to maintain their style of play.

Chris Wilder with assistant Alan Knill credit: REUTERS

Bournemouth are a pacy team built to hit opponents on the counter and Chris Wilder's cautious switch from a 3-4-1-2 to a 3-5-2 at the Vitality Stadium on opening day showed a willingness to adapt. By adding an extra body to midfield United avoided being overrun, with Billy Sharp's late goal securing a 1-1 draw.

"If you look at last season we conceded the least goals (joint-best with 41) and [had the best goal difference in the Championship]. This system is how we play - we’ve played it for three years now, and it works".

It works in the Premier League

Crystal Palace became the first Premier League side to be punished by an overlapping centre-backs move this season, conceding the only goal of the game at Bramall Lane.

David McGoldrick passes back to O'Connell in defence as Palace sit with a deep defensive line. United have possession and can therefore look for an overload.

Sheffield United vs Palace overlapping centre-backs

O'Connell takes the hint and sprints down the left wing.

O'Connell on the overlap

O'Connell overlaps before playing a one-two with left wing-back Enda Stevens, who has moved into a central attacking position.

O'Connell

Palace right-back Joel Ward now has a two vs one to defend again because Luke Freeman is close by.

Freeman

O'Connell's overlap causes a half-second of confusion, allowing Freeman to steal the reverse pass from Stevens and dribble past the off-balance Ward, passing low across the box to set up John Lundstram.

Lundstram goal

Lundstram scores.

How Sheffield United defend

Although a back three with wing-backs in possession, out of possession Sheffield United switch to a back four. The wing-back engages the opposition winger early "to apply pressure", Knill explains, as a centre-back moves to the full-back position.

As the opposite side wing-back drops to support, the back three becomes a four, allowing Wilder's team to double up in wide areas and gain numerical advantage, blocking the centre of the pitch too.

Clever tactics and gameplans have helped Sheffield United earn promotion twice in three seasons playing an entertaining brand of expansive football. Overlapping centre-backs in a possession-based setup worked wonders in the Championship, and Knill says those who invented it hope the system will be successful in the Premier League too.

As Crystal Palace have already learned, it certainly seems to work.