In what was a very successful season for RGC Nice last year, Claude Puel is generally held to have fielded a midfield diamond, but based on the impressive 6-1 victory over Bordeaux last season, it might have been more like a very fluid 4-3-3 with Hatem Ben Arfa deployed as one of the more modern tactical phenomena, a 'false nine'.
The tactic- an attacking player who appears to be playing centre forward but drops deeper than a central striker typically would- was most famously utilised by Barcelona under Pep Guardiola, as a means of moving Lionel Messi from the periphery of play to areas from which he would become the fulcrum of the team. This meant that first Samuel Eto'o and then David Villa- two of Europe's most accomplished finishers- were shunted out to the left of the forward line. Both men are natural strikers and neither seemed to particularly relish the role, despite continuing to be fairly prolific. It seems likely that the resentment stemmed at least partly from egos bruised by not being the team's focal point. It's not as if they were expected- as Eto'o later would be at Jose Mourinho's Inter- to be shuttling up and down the touchline in perpetuity. In Guardiola's system they were not wingers, more wider attackers, closer to the old fashioned inside forwards common in the years before 4-4-2- and other systems that made use of two out-and-out strikers- established hegemony.
Ben Arfa's play in the Bordeaux game wasn't entirely unlike that of Messi, as he dropped deep and darted wide, essentially in pursuit of space and, more to the point, possession. However Ben Arfa's role might have been defined, Puel's thought process was probably the same as Guardiola's; field the best player in the position in which he was most able to get a lot of the ball.
When Nice were in possession, their other main attackers- Valere Germain and Mickael Le Bihan- played as central strikers tend to when there are two of them; in the channels between centre backs and full backs. When defending though (see image below), they would move wider to restrict balls out to players on either side, leaving Ben Arfa, as the furthest player forward, to press the centre backs (which he did with a gusto that might have surprised Newcastle fans who would often bemoan his defensively listless displays). Valerie too bought into the strategy wholeheartedly, constantly chasing and cleverly curving his runs in order to cut off as many passing options as possible for the Bordeaux defenders as they tried to play out. It's no surprise that there is speculation that Puel might be keen for Saints to recruit him, as he looks well suited to the style of play.
In the recent friendly against Zwolle, Saints' shape was similar, with Nathan Redmond in the Ben Arfa role. The next photo shows Redmond as the most advanced Saints player when the opposition had the ball, with Jay Rodriguez and Charlie Austin either side of him.
What Puel or anyone else wants to call the system is unimportant; it was undeniably effective, not to mention entertaining. The fluidity of the front three (or, if you like, two and a half) was underpinned by a midfield three with a single pivot that were aggressive as well as organised and compact, with marauding fullbacks Jeremy Pied (another player linked with Saints) and Ricardo providing width. As with Mauricio Pochettino's Southampton side, they occasionally looked vulnerable to long balls played into the areas vacated by Pied and Ricardo, but were generally adept in transitions between attack and defence.
The very fact that there's confusion about what the formation is suggests a move back towards the vivacious, liberated football played under Pochettino and away from the more rigidly structured play of Koeman's teams. To play with such apparent freedom tends, paradoxically, to come from constant, repetitive work on the training pitch, so with internationals gradually filtering back after the Euros there may be a few teething problems, but although the age group teams at Southampton tend towards 4-2-3-1 rather than whatever exotic system Puel might intend on adopting, the club's player recruitment and development prioritises the kind of athleticism required for the high press and quick transitions, as well as the technical excellence necessary for the sort of sharp passing displayed by Puel's Lyon.
Diamond or not, everything looks to be in it's right place, wherever the places may be.