Prerequisite: requires goliath
When you hit a creature with a Headbutt attack, the creature's speed becomes halved for the rest of the turn.
Creatures provoke opportunity attacks from you even if they take the Disengage action before leaving your reach.
When a creature within 5 feet of you makes an attack against a target other than you (and that target doesn't have this feat or Sentinel), you can use your reaction to make a Headbutt attack against the attacking creature.