Heretical Gaming blog, JWH was wondering how to incorporate squares into Neil Thomas's Simplicity in Practice rules, but doing so without actually changing formations (since the rules use single-base units) or using markers.
I suggested a couple of ideas in the comments, but having now played a couple of games and read through the design notes I think I have come up with something simple an workable.
The rules already penalise cavalry from charging infantry frontally, by giving the infantry a combat bonus. In addition only one unit may ever engage an opposing unit in melee. So I thought that I would work with these two factors.
So, my idea is this. Before melee is resolved, COI that have been charged in the flank by HC, DG or LC may make a roll to see if they can 'form square'. This succeeds on a 3+, and allows the COI to immediately turn to face the cavalry. However subtract 2 from the roll if the cavalry are eligible to receive support from at least one friendly ART or COI unit.
The rationale behind this is as follows. Cavalry are penalised if they attack COI frontally, so flank attacks become attractive. 'Square' basically allows the COI to avoid flank attacks and put the cavalry at a disadvantage. The roll covers whether the unit forms it in time. You could adjust it for unit quality if you like, but see below. However squares are vulnerable to enemy infantry and/or artillery, so I make the roll harder to achieve of the enemy cavalry is supported by such troops.
I did consider adding in a modifier based on how many DP the infantry unit has, but these are already factored into the melee calculation anyway. To some extent the rules for unit quality factor this in as well, so can be excluded from the roll on that basis.
I have tried to keep the rule, and the thinking behind it, in keeping with the original design parameters and the Neil Thomas Way of Doing Things. The next step is, of course, to try it out in an actual game.