When a unit is charged in the flank or rear it is usual to turn any individual models that are fighting to their side or rear so they are facing their attackers. This doesn't mean the unit is turned or that it is facing a different direction, just the models which are actually touching an enemy. The combat bonuses for attacking in the flank or rear still apply.

It can happen that if a unit is small, and is deployed in one rank, all of its models are turned to face an attack from the rear because all of its models are touching their attackers. The unit is charged in the rear, the chargers are moved in against their backs, and the individual models are turned to face. In this case the chargers do receive the combat bonus for attacking in the rear but only in the first turn of fighting. This is because it becomes rather confusing to do otherwise, while the unit is obviously sufficiently small to effect a turn without undue disorder in the ranks. A one turn penalty is therefore both an appropriate and effective solution.