Attacks of opportunity are important to the overall balance of the D&D combat rules. They're also a little bit confusing and easy to ignore. One of the many, many goals of D&D 3.5 is to deal with issues just like that. The new combat chapter is both shorter and easier to understand than the earlier version. As an example of the type of change we're talking about, here's the new description of attacks of opportunity.
As always, remember that nothing is complete or final until you buy the book in the store.
Attacks of Opportunity
The melee combat rules assume that combatants are actively avoiding attacks. A player doesn't have to declare anything special for her character to be on the defensive. Even if a character's miniature figure is just standing there on the battle grid, you can be sure that if some orc with a battleaxe attacks the character, she is weaving, dodging, and even threatening the orc with a weapon to keep the orc a little worried for his own hide.
Sometimes, however, a combatant in a melee lets her guard down, and she doesn't maintain a defensive posture as usual. In this case, combatants near her can take advantage of her lapse in defense to attack her for free. These free attacks are called attacks of opportunity.
Threatened Squares: You threaten all squares into which you can make a melee attack, even when it is not your action. Generally, that means everything in all squares adjacent to your space (including diagonally). An enemy that takes certain actions while in a threatened square provokes an attack of opportunity from you. If you're unarmed, you don't normally threaten any squares and thus can't make attacks of opportunity (but see Unarmed Combat).
Reach Weapons: 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 (such as a longspear) threaten more squares than a typical creature. For instance, a longspear-wielding human threatens all squares 10 feet (2 squares) away, even diagonally. (This is an exception to the rule that 2 squares of diagonal distance is measured as 15 feet.) In addition, most creatures larger than Medium have a natural reach of 10 feet or more; see Big and Little Creatures in Combat.
Provoking an Attack of Opportunity: Two kinds of actions can provoke attacks of opportunity: moving out of a threatened square and performing an action within a threatened square.
Moving: Moving out of a threatened square usually provokes an attack of opportunity from the threatening opponent. There are two common methods of avoiding such an attack -- the 5-foot-step (see Miscellaneous Actions) and the withdraw action (see Full-Round Actions).
Performing a Distracting Act: Some actions, when performed in a threatened square, provoke attacks of opportunity as you divert your attention from the battle. Casting a spell and attacking with a ranged weapon, for example, are distracting actions. 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. For instance, a character with the Improved Unarmed Strike feat doesn't incur an attack of opportunity for making an unarmed attack.
Making an Attack of Opportunity: An attack of opportunity is a single melee attack, and you can only make one per round. You don't have to make an attack of opportunity if you don't want to.
An experienced character gets additional regular melee attacks (by using the full attack action), but at a lower attack bonus. You make your attack of opportunity, however, at your 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).
Combat Reflexes and Additional Attacks of Opportunity: If you have the Combat Reflexes feat, you can add your Dexterity modifier to the number of attacks of opportunity you can make in a round. This feat does not let you make more than one attack for a given opportunity, but if the same opponent provokes two attacks of opportunity from you -- such as by moving out of a threatened square and then casting a spell in a threatened square -- you could make two separate attacks of opportunity (since each one represents a different opportunity). 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. All these attacks are at your normal attack bonus. You do not reduce your attack bonus for making multiple attacks of opportunity.
Finally, there'll be a diagram to go along with this explanation of attacks of opportunity, but it's not available yet. So instead, we'll share a pair of critters whose threatened spaces you'd rather not invade -- the balor and marilith.
Dragon Magazine features monthly focus articles on the upcoming D&D 3.5 revision. For more information on changes to the haste, harm, and hold person spells, check out Dragon 307 (May), available on newsstands April 22, 2003. Or subscribe to Dragon for your monthly fix of the latest Dungeons & Dragons updates and meaty bonus features.
Hear Ed Stark Discuss D&D 3.5!
Ed Stark appeared on Mortality.net Radio on March 28, 2003, to discuss the D&D 3.5 revision that releases in July of this year. His show, nearly 3 hours of nitty-gritty information about the upcoming revision, is available for download or streaming on their site. Consult their site for streaming information, or download the MP3 if you have a fast connection. The file is 30 MEG, but you won't want to miss it!