Since the formation of the Premier League in 1992, various different formations have dominated.
The 4-4-2 has long been considered English football's default system, although there was a brief craze of 3-5-2 in the mid-to-late 1990s. Jose Mourinho's impact in the mid-2000s meant many sides shifted to 4-3-3, before 4-2-3-1 started to become the most common system in the early 2010s. A couple of years ago, 3-4-3 became suddenly popular after the brief dominance of Antonio Conte's Chelsea.
One major system that has never enjoyed a period of dominance, however, is the midfield diamond. This is somewhat strange: it's not a million miles away from the 4-4-2, essentially just about squashing the midfield quartet together. In fact, the system that brought England their only World Cup success, 52 years ago, was effectively a diamond with Bobby Charlton at the tip of Alf Ramsey's "wingless wonders." Yet when Sven-Goran Eriksson found himself with Paul Scholes, Frank Lampard, Steven Gerrard and David Beckham and tried playing all four centrally in a diamond, the players collectively complained and lobbied for a return to 4-4-2.
In the Premier League, both Mourinho in 2004 and Carlo Ancelotti used a diamond with initial success before switching to 4-3-3. Sir Alex Ferguson briefly used it during Manchester United's title-winning campaign of 2012-13, but it never entirely worked. Brendan Rodgers and Liverpool played it effectively the following campaign, but more as an alternative to the 4-3-3.
For one reason or another, the diamond just isn't popular in England. The shape has some problems (the lack of permanent width, in particular) but it's a useful system for dominating the centre of the pitch. It also allows a goal-scoring midfielder to push forward and make "third man runs," something English football traditionally loves.
The last month has demonstrated the positives of the system and there's a good chance that Arsenal's meeting with Manchester United this Friday in the FA Cup fourth round (2:55 p.m. ET, ESPN+) will feature both teams playing with a midfield diamond.
Since Ole Gunnar Solskjaer took charge of Manchester United in December, his most interesting tactical move was the decision to switch to a diamond against Tottenham Hotspur in a 1-0 victory earlier this month. He had previously stuck to a 4-3-3 but was fearful of his players being overrun in midfield by the diamond shape used by Mauricio Pochettino.
Spurs were performing excellently in that system, with Harry Kane leading the line, Son Heung-Min running into the channels, Dele Alli pushing forward to support them. Therefore, Solskjaer decided to play Spurs at their own game, matching Pochettino's diamond. Jesse Lingard moved inside from his right-wing position to occupy Harry Winks, with Marcus Rashford and Anthony Martial playing up front, spreading wide and attacking into the channels.
In the first half it worked sensationally and Rashford's winner came courtesy of a specific move that Paul Pogba, who provided the assist, admitted United had worked on in training that week. In the second half United suffered, and relied upon David De Gea to see out the game. It was, nevertheless, the first sign of Solskjaer's tactical acumen.
Last weekend, meanwhile, Arsenal produced arguably their most convincing performance of the season -- once you consider the quality of the opposition -- and confidently defeated Chelsea 2-0. Their victory owed much to Unai Emery's decision to start with a diamond for the first time in the Premier League this season, having previously considered it only as a Plan B in the second half. (He used it in the 4-2 win over Tottenham, for example.)
Having repeatedly struggled in the first half of matches, Arsenal were excellent in the first 20 minutes against Chelsea: pressing aggressively in numbers and breaking quickly into the channels. Aaron Ramsey was deployed in a man-marking role on Jorginho, who saw little of the ball in the opening stages, while Alexandre Lacazette and Pierre-Emerick Aubameyang both showed a willingness to track back in addition to combining dangerously going forward.
Arsenal lack players who are comfortable out wide and those positions have generally been filled by the likes of Ramsey, Mesut Ozil or Henrikh Mkhitaryan, who all prefer playing as the No. 10. The desire to accommodate both Lacazette and Aubameyang means the latter has also been fielded out wide and out of position. Alex Iwobi is the closest thing to a natural winger, and he intelligently combines with overlapping wing-backs, but even he's actually more comfortable as a No. 10 as well.
Therefore, the diamond suits Arsenal well, and after last week's positive performance against Chelsea, it would be somewhat surprising if Emery moved away from that system against Manchester United. And because United dealt with Spurs' diamond by matching it, the obvious riposte will be United playing in a diamond too, with Lingard in the middle. This will be something of an unprecedented situation in this fixture considering that Arsenal and United have spent the past two decades depending on width from midfield.
Contests between two sides using a diamond can be unattractive: with so many players in the centre, forward passes can be difficult. The obvious "out ball" is a lateral pass toward the full-backs, who are the freest players on the pitch but usually not the most creative options. But the diamond becomes more dynamic when you consider the attackers likely to start at the Emirates.
Arsenal's Lacazette and Aubameyang are both speedy forwards who cover wide areas effectively; the same is true of United's Martial and Rashford. These modern centre-forwards work excellently in this system by providing width and offering a threat in the channels, exploiting any forward movement from the opposition full-backs and pouncing at transitions.
Usually, diamond vs. diamond is a clash of two different systems that provides tactical intrigue. This weekend, however, Arsenal's and United's shifts toward the same approach could prove fascinating.