Combat reactions allow you to take certain actions when it is not your turn. You gain your first combat reaction at BAB +0. At BAB +6, BAB +11, and BAB +16, you gain an additional combat reaction each turn. Any condition that prevents you from making an attack of opportunity prevents you from using a combat reaction.
You may assist another character’s melee attack on his turn. If you’re in position to make a melee attack on an opponent that is engaging a friend in melee combat, you can aid your friend as a combat reaction. Before your friend makes his attack roll, announce your intention to use your combat reaction to Aid Attack. Your friend gains a +2 bonus on his attack roll. Multiple characters can aid the same friend, and the bonuses stack.
You may assist another character’s defense. If you’re in position to make a melee attack on an opponent that is engaging a friend in melee combat, you can aid your friend as a combat reaction. On the opponent’s turn, before he makes his melee attack roll against your friend, announce your intention to use your combat reaction to Aid Defense. Your friend gains a +2 bonus to his AC against that attack. Multiple characters can aid the same friend, and the bonuses stack.
You may attempt to dodge a single melee or ranged attack. On the opponent’s turn, before he makes his attack roll against you, announce your intention to use your combat reaction to Dodge. Against that single attack, you gain a dodge bonus to your AC equal to ½ your BAB.
If you are engaged in melee, you may use your combat reaction to block your opponent’s melee attack. On the opponent’s turn, before he makes his attack roll against you, announce your intention to use your combat reaction to Block. Against that single attack, you gain DR against that attack equal to ½ your BAB. If you are blocking with a buckler or shield, add the shield’s AC bonus (including any enhancement bonus) to the amount of DR. If you have DR from another source, the DR from block stacks with your highest applicable DR.
Attack of Opportunity
As a combat reaction, you may make a single melee attack at your normal attack bonus against an enemy that provokes an attack of opportunity in your threatened area. See the Attack of Opportunity section for information on your threatened area and provoking an attack of opportunity.
Provoking an Attack of Opportunity
Two kinds of actions can provoke attacks of opportunity: moving out of a threatened area, and performing certain distracting actions while within a threatened area.
Moving: Engaging with an opponent does not provoke an attack of opportunity; disengaging with an opponent does. Moving into an opponent’s threatened area engages you with that opponent; moving out of that opponent’s threatened area then disengages you from that opponent (unless that opponent is still within your own threatened area—in which case you are still engaged). If you are engaged with an opponent, and any part of your movement disengages you from that opponent, you provoke an attack of opportunity.
There are two common methods of avoiding an attack of opportunity: the 5-foot step and the withdraw action.
Performing a Distracting Action: Some actions, when performed in a threatened area, provoke attacks of opportunity as you divert your attention from the battle. Table 8–2: Actions in Combat notes many of the actions that provoke attacks of opportunity. Remember that even actions that normally provoke attacks of opportunity may have exceptions to this rule.
Making an Attack of Opportunity: An attack of opportunity is a single melee attack, and you must use a combat reaction to take one. You don’t have to make an attack of opportunity if you don’t want to.
You make an attack of opportunity at your full normal attack bonus—even if you’ve already attacked in the round.
An attack of opportunity “interrupts” the normal flow of actions in the round. If an attack of opportunity is provoked, immediately resolve the attack of opportunity, then continue with the next character’s turn (or complete the current turn, if the attack of opportunity was provoked in the midst of a character’s turn).