Unarmed Attacks
Striking for damage with punches, kicks, and head butts is much like attacking with a melee weapon, except for the following:
Attacks of Opportunity
Attacking unarmed provokes an
attack of opportunity from the character you attack, provided she is armed. The attack of opportunity comes before your attack. An unarmed attack does not provoke attacks of opportunity from other foes nor does it provoke an attack of opportunity from an unarmed foe.
An unarmed character can't take
attacks of opportunity (but see
"Armed" Unarmed Attacks, below).
"Armed" Unarmed Attacks
Sometimes a character's or creature's unarmed attack counts as an armed attack. A
monk, a character with the
Improved Unarmed Strike feat, a spellcaster delivering a
touch attack spell, and a creature with natural physical weapons all count as being armed.
Note that being armed counts for both offense and defense (the character can make
attacks of opportunity)