If the enemy has fled, or if you have estimated your charge incorrectly, your troops might not be able to move far enough to reach their intended target. If this is the case the charge has failed.
If a charge fails the unit is moved at its normal movement rate rather than its double speed charge. The unit is moved directly towards the intended target as if it were charging but halts once it has covered its normal move distance. This represents a situation where troops have begun to charge before realising it is impossible to reach their enemy; consequently their movement peters out and they lose impetus and enthusiasm.
A unit that fails its charge cannot shoot with missile weapons that turn.