The character is a skilled unarmed combatant. Unarmed strikes deal
1d4 damage (or 1d3 off-hand) plus STR modifier, instead of the
ordinary 1d2 + STR. Unarmed strikes do not provoke an attack of
opportunity. An unarmed natural 20 stuns the target for 1 round.
Stun immunity still applies. See player CH-10, Unarmed attacks.