WHY 4-2-3-1
To understand this one needs to delve into the situation Pioli arrived in Milan at. When Giampaolo was sacked and Pioli was appointed as the coach of Milan he joined a team that was vastly an unknown quantity not just to him but among themselves. So he stuck with the formation used by the previous coaches, the 4-3-3 formation. However as we all know it all culminated with the rout at Bergamo with Atalanta trashing Milan 5-0 and a huge out cry for tactical changes being called for.
Before the match at Bergamo a few points became amply clear to Pioli
- Theo Hernandez has enormous potential to play as a pseudo left winger and can even score goals (was Milan’s top scorer until Februaruy)
- Kessie is best utilized as a Defensive midfielder who can make a few runs but he is not the best with his creativity or on the ball skills.
- Romagnoli is not the best defender when dealing with pacy wingers or strikers and with midfielders expected to make runs to support the forwards in a 4-3-3 and with attacking it creates a “corridor of uncertainty” on the left

Bennacer is not an apt player to play as a holding midfielder in a single pivot.
These factors and the 5-0 defeat played on Pioli’s mind and it made him want to change the formation to make sure he keeps up the pressing but also provide help for the attackers in the wide area
After analyzing Flick’s Bayern, Pioli decided to switch to a 4-2-3-1 and this utilized his team’s strength the best by
With a double pivot it gave extra security to Pioli to guard against counter attacks which is one of the 4-2-3-1’s main strength.
Kessie being to the role of a defensive midfielder on the left side covered the earlier mentioned corridor and it allowed the defense to keep its structure allowing Theo to sprint forward and Romagnoli an extra cover

Kessie’s change of role also helped Bennacer to have more freedom having been liberated from having to shoulder the entire responsibility of screening the defense and it helped him to make those runs into the attacking third
Theo got to join the attack and underlap/overlap the left sided winger.
And of course with Zlatan being signed he gave Pioli a striker to play off or a target man to aim crosses and even hold up play for Theo to make runs off.
Fast forward to 2021/22 season Milan are seemingly going to lose Kessie and Romagnoli on a free transfer after Milan lost Hakan as well. Milan have already secured Yacine Adli from Bordeaux who is a hybrid of a #8 and a #10.

There have been talks of Milan switching to a 4-3-3 and the average positioning map against Napoli seems to suggest the same. Here is why a 4-3-3 would be a natural evolution for Milan

- A 3 man midfield would give Milan a midfield superiority. When Milan played with a 4-2-3-1 it needed the natural #10 i.e Diaz or Hakan to sit back with the double pivot whenever they lost the ball the make sure they don’t get numerically beaten in the midfield as they seemed to be against teams that play a 3-5-2 or a 4-3-3.
- It gives Milan more control in midfield and helps them play more fluid football with more options in midfield.
- It takes away a chunk of responsibility of creativity and the need to connect defense from attack by the #10
- With no Kessie who did not display the best of his abilities as a mezalla. If Milan can pull off the signing of Renato Sanches or another attacking midfielder then Milan will have extra midfield players who can make runs into the box and hence extra attacking options which can be difficult to defend for the opposition.
- This team is into Year 3 of their project with Pioli and Maldini. They have created a good environment of trust and they know each other’s movements very well. Along with this the players and manager are in total harmony with each other. It helps for more options
- With Theo more mature and selecting his moment to attack carefully and not bomb at every opportunity there is less opportunity for opposition to counter
- With Romagnoli being seemingly replaced by Tomori who is one of the fastest and most aggressive center backs in Serie A once again that corridor of uncertainty is closed.
- Bennacer, who like Theo has matured, has shown how he can cover lots of ground and contribute to attack with runs like the one he made against Napoli (when Kouilybaily fouled him) is also ready
- With a vibrant midfielder like Tonali who also covers a lot of ground and can run at top speeds of 35 kmph can act well as a midfielder in the single pivot and single handedly screen the defense and recover lose balls when Milan play a high line
- It gives Milan more passing combinations and more options to create passing triangles and/or Passing diamonds to go past opponents.


CONCLUSION
Of course this is only a tactical theory on a personal level and there is yet a lot of games to come this season plus an entire summer market which can dictate the game plan for next season. One thing is for sure, Pioli has given a thought to the system and Milan did try it out (albeit to neutralize Napoli’s midfield) one wonders if signings like Renato Sanches and Adli signals a change of things.