Headbutt:
A surprise head attack! If the attack succeeds, the victim takes normal damage to a random head location.

Critical hits break bone. Unsuccessful attacks result in both attacker and victim taking 1/3rd normal damage to heads.

Critical failures result in the attacker taking their full normal damage to a random head location.

If the attacker's STR is twice that of the victims STR, then the victim is automatically stunned on a successful hit (armour etc. prevents this).