Rage Fist inflicts damage. Its power increases by 50 each time the user is hit during the battle by a move that causes direct damage, up to a maximum of 350 (after 6 hits). This includes moves by either allies or opponents, and does include moves that do not actually deplete HP (such as when Disguise activates), but does not include self-inflicted confusion damage, nor moves that merely hit the user's substitute. Each strike from a multi-strike move counts as one hit. Switching out or fainting does not reset the hit counter. Transform copies the targets hits counter.
A Primeape that has used Rage Fist at least 20 times evolves into Annihilape when leveled up. Rage Fist does not need to hit in order for the required evolutionary condition to be met. However, it will not be met if Rage Fist could not be executed because of paralysis, confusion, infatuation, flinching, or Disable.