In the APG new rage powers, I found this one:
Ferocious Trample, Greater (Ex): A barbarian’s mount can affect creatures up to its own size with its ferocious trample. In addition, it can make an overrun combat maneuver check as a free action against a creature that fails its Reflex save (or chooses not to save in order to take an attack of opportunity) against its trample. A barbarian must have the ferocious trample rage power to select this rage power. A barbarian must be at least 12th level to select this rage power.
If trample is an attack that does not require a check, why the mount get an overrun combat maneuver? Does it not overrun the trampled target automatically?