The melee combat rules assume that combatants are actively avoiding attacks. Sometimes combatants in a melee let their guard down. In such cases, other combatants nearby can take advantage of the lapse in defense to attack for free. These free attacks are called attacks of opportunity.
If you’re considered armed, you threaten all squares into which you can make a melee attack, even when it isn’t your turn. That usually means everything in all squares adjacent to your space, including diagonally. An enemy that undertakes certain activities while in a threatened square provokes attacks of opportunity. If you’re considered unarmed, you don’t normally threaten any squares and thus can’t make attacks of opportunity. Certain conditions in combat, such as concealment and cover, also affect your ability to make attacks of opportunity.
Most creatures of Medium or smaller size have a reach of only 5 feet. This means that they can make melee attacks only against creatures up to 5 feet (1 square) away. However, Small and Medium creatures wielding reach weapons might threaten more squares than a typical creature. Creatures larger than Medium have a natural reach of 10 feet or more, so they
threaten all squares within that reach, including diagonal ones. Creatures smaller than Small typically have a natural reach of 0 feet, meaning they can’t reach into adjacent squares. Since they have no natural reach, such creatures don’t threaten the squares around them at all.
PROVOKING ATTACKS OF OPPORTUNITY
Moving out of a threatened square can provoke attacks of opportunity, as can being in a threatened square while performing an act that requires focused attention.
Moving out of a threatened square usually provokes an attack of opportunity from any opponent who threatens that square. Two methods of movement allow you to avoid such an attack: 5-foot step and withdraw. See Movement.
Moving out of more than one square threatened by the same opponent in the same round doesn’t count as more than one opportunity for that opponent.
When you focus your attention on what you’re doing, you divert your attention from the battle. The Actions in Combat table, notes many activities that provoke attacks of opportunity for this reason. Some such actions allow you to make a Concentration check to avoid provoking (see
Concentration). Even actions that normally provoke attacks of opportunity can have exceptions.
MAKING ATTACKS OF OPPORTUNITY
An attack of opportunity is a single melee attack you can make when you’re active in combat and an opportunity presents itself. If you’re fl at-footed, you can’t make attacks of opportunity, and you don’t ever have to make an attack of opportunity if you don’t want to. Making an attack of opportunity isn’t considered an action, but you can make only one attack of opportunity per round unless you have an attribute that allows you to make more (see below). If you have multiple attacks for some reason, you use your highest normal attack bonus when you make your attack of opportunity, even if you’ve already attacked during the round.
An attack of opportunity interrupts the normal flow of actions in the round. If an attack of opportunity is taken, immediately resolve that attack of opportunity, then continue with whatever was happening when the attack of opportunity was provoked.
Multiple Attacks of Opportunity
Some abilities allow you to make more than one attack of opportunity per round. Most such abilities, unless they say otherwise, don’t let you make more than one attack for a given opportunity. If the same opponent provokes two attacks of opportunity from you, however, you could make two separate attacks of opportunity. Each provoking act represents a different opportunity. Multiple attacks of opportunity otherwise follow the rules for normal attacks of opportunity.