If you want to win the Premier League title, it seems there's a peculiar ritual you have to follow — lose by three goals to Arsenal in late September.
Last season, Claudio Ranieri's Leicester City were thrashed 5-2 by Arsenal at the King Power Stadium, with Alexis Sanchez helping himself to a hat trick. 363 days later, Arsenal produced another masterful performance to thrash Antonio Conte's Chelsea 3-0, with Sanchez and Mesut Ozil counter-attacking majestically through Chelsea's backline.
This is ultimately a complete coincidence, but both results have proved significant in transforming the fortunes of Leicester and Chelsea respectively. It forced both their managers to reformat their sides significantly, therefore creating the most cohesive — and, in particular, the most defensively solid — teams in the Premier League.
The significance of Leicester's 5-2 defeat by Arsenal went somewhat unappreciated — the match wasn't televised in Britain, and at that point no one had deduced that Leicester were actually serious title challengers. But the severity of the defeat meant Ranieri changed his system drastically, ditching both his previous first-choice full-backs.
Jeffrey Schlupp, who won the club's Players' Player of the Season award the previous season and had excelled at wing-back, found himself less comfortable as a conventional full-back and constantly left large gaps behind him. On the right, however, Ritchie De Laet was caught out of position which often left space for the opposition to break into.
Ranieri instead turned to Christian Fuchs, a more solid left-back who stayed in position, and the combative Danny Simpson on the right. They were given very specific instructions: only overlap when Leicester are losing, and chasing the game. It transformed Leicester's season: suddenly, both Robert Huth and Wes Morgan looked more solid, with less space to cover in the channels.
"Jeff and Ritchie going forward are lightning," explained goalkeeper Kasper Schmeichel. "But it left huge, huge spaces to be exposed in behind…we needed to change something. Now we have four defenders in there."
Fast-forward a year, and with Chelsea trailing 3-0 at the Emirates, Conte changed their system entirely. Chelsea's 4-1-4-1 had been ripped apart, so he shifted to a 3-4-3 system instead. Off went Cesc Fabregas — to huge jeers from Arsenal supporters — and on came Marcos Alonso for his Premier League debut. He'd been signed specifically because he was comfortable playing as a wing-back, while David Luiz's return was partly due his comfortability playing in a back three.
From then, Chelsea narrowly failed to break Arsenal's 14-year-old record for the most consecutive wins, have never returned to the three-man defence, and have seemingly made themselves nailed-on title favourites.
"We started the season with another system, but I noticed in some circumstances we didn't have the right balance," Conte said. "For this reason, we switched to the new system of 3-4-3 and I think this is a good fit for our squad because we have the forwards adapted for this system." But, equally crucially, they had the right type of defenders too.
The fact that the opposition was Arsenal is peculiar but ultimately irrelevant. What's significant, though, is that both managers realised how vulnerable their side was to counter-attacking, particularly by opponents exploiting the gaps between centre-backs and full-backs. As teams increasingly play neat, technical football reliant upon through-balls in behind defenders, and their opponents increasingly use their full-backs as attacking weapons rather than defensive players, exploiting that space has become one of football's most notable features.
It's rare to see a move that penetrates the opposition's back four that doesn't utilise that space in some way, whether through the attackers' run or the through-ball. Sometimes, like for Danny Welbeck's goal for Arsenal against Liverpool last weekend, both ball and run go between those two players.
Ranieri and Conte, of course, changed in two completely different ways. Ranieri's system was simply modified to include players to tuck in more, whereas Conte changed the system entirely. But the basic idea was essentially similar: to stop opponents from finding space in the channels. Few have caused Chelsea's back three problems on the break since, in part because the gaps are now on the wings close to the touchlines, rather than in the channels running closer to goal.
It's also worth remembering that Pep Guardiola's peculiar experiment of using full-backs drifting inside into midfield positions was partly for a similar reason — he released that when full-backs push forward towards the corner flags to stretch the play, they have little chance of quickly recovering their defensive positions. Guardiola asked his wingers to stretch the play and provide constant width, which meant the full-backs could take more conservative positions on the outside of, effectively, a midfield trio.
That meant they could transition to defence quicker and minimise the space in the channels, making it tougher for the opposition to break into. It worked better with Bayern Munich, where Philipp Lahm and David Alaba had experience playing in central midfield anyway, rather than at Manchester City, who lacked the requisite players. The idea, however, makes a lot of sense.
In basic terms, there seems to be little between Ranieri, Conte and Guardiola's adjustments. But they are essentially three completely different ways of guarding against the same problem: leaving too much space in the channels. It's another small reminder of football's eternally evolving tactical landscape, and another illustration of the strategic versatility in the Premier League.