If both sides wish to make (or attempt to make) a combat reform, take any Leadership tests required in order to make the reforms, then roll off to determine which side makes all of their reforms first (the winner of the roll-off decides).
If a unit is engaged to more than one facing (say to the front and one flank), it cannot make combat reforms.
In case multiple units are involved in the same combat and one unit flees, any combat reforms attempted are done after all pursuit attempts are finished.
In some cases, most likely because a unit previously engaged in combat has broken off or similar, two units might find themselves only partially engaged in base contact with some models in the front rank not fighting. In these situations, the unit with the lower Unit Strength must be moved sideways until all models in either unit's front rank is in base contact with the other unit. This is done after any other reform has been performed.