Attacks of Opportunity

Sometimes, a melee combatant lets their guard down to execute a non-combat action. In these circumstances, combatants near them can take advantage of this lapse in defense to make a free attack. These attacks are called attacks of opportunity
 * Threatened Area: If you have a weapon equipped (or are unarmed and have the [[Improved Unarmed Strike[[ feat), you threaten the area into which you can make a melee attack. Generally, that’s everything that’s in your 120 degree forward arc and within five feet of you. An enemy that takes certain actions in a threatened area provokes an attack of opportunity from you.
 * Provoking an Attack of Opportunity: If you move into, within, or out of a threatened area, you usually provoke an attack of opportunity.
 * Some actions themselves provoke attacks of opportunity.
 * Attacking with a ranged weapon
 * Attacking unarmed (without the Improved Unarmed Strike feat)
 * Casting a spell
 * Activating a ‘spell completion’ magic item like a scroll
 * Using a spell-like ability
 * Running
 * Some feats
 * Making an Attack of Opportunity: An attack of opportunity is a single melee attack nade at your normal attack bonus. You can only make one attack of opportunity per round.