On the Formations screen, when you stop the mouse over a square on the pitch it says the zone of the square and the mentality, ie zone:A Mentality:0 or mentality:1 or mentality:-1

What is this mentality for?

read the RS wiki’s. It’ll explain everything. just go to the wiki and type in mentality and check out the description. I find the wiki’s quite useful.

but basically: -1 for defensive, 0 for neutral and +1 for offensive, for each player.