Damage an enemy by running over it with whatever steed you happen to be riding. A fast, cheap skill, but not spectacular damage wise, especially if riding a sheep.

The in game help reads:

Skill duration: 2.
Type of skill : offensive skill.
Party rows    : 1st.
Affecting stats: Dex.
It uses 10 endurance points.
The mere mass of a rider and his mount can be enough to crush his opponents
underfoot (or hoof, as the case may be). A skilled rider can use his steed's
weight as a weapon, either with a running start or by rearing up. Either way,
the effect can be devastating. Of course, knowledge of combat riding is
required for effective use of this skill.