If the target unit declares a Flee! reaction, the charging unit now has a choice: it can either attempt to complete the charge against the now-fleeing unit, or try to redirect its charge by making a Leadership test. If the test is failed, the charging unit must attempt to complete the charge against its original target. If the test is passed, however, the charging unit can declare a fresh charge against another viable target (the chargee may declare a charge reaction as normal). If there are no other suitable targets to charge, a charging unit cannot test to redirect.
Each unit can only make one redirect per turn.