It sometimes happens that pursuers move so far that they hit a fresh enemy unit. The pursuers are carried forward against the enemy unit as they chase their fleeing enemy. This is treated as if it were a new charge. The pursuing unit has no choice in the matter, they must charge against the fresh enemy. The unexpectedly attacked unit can only respond to the charge by 'holding'; any attempt to flee, shoot, Or do anything else amidst the confusion of running bodies is deemed impossible.
The resulting combat is worked out in the following turn. The pursuers are charging and so get all the usual benefits and bonuses as if they had charged that turn, even though their charge actually occurred during the close combat phase of the previous turn.
Assuming pursuers do not encounter any fresh enemy they move the distance indicated by their dice roll and thereafter are ready to fight normally. So, in their following turn they may charge, march or move normally exactly like any other unit, and no penalty is imposed because of their pursuit move.