DnD Opportunity Attacks Rules
Opportunity attacks are one of the most tactically significant rules in Dungeons & Dragons 5th Edition — a single triggered reaction that can shift the outcome of an entire encounter. This page covers the exact definition, the mechanical steps involved, the situations where opportunity attacks apply (and where they don't), and the decision points that separate a competent tactician from someone who just learned what a reaction is. Whether a player is dodging a sword-wielding gnoll or a Dungeon Master is adjudicating a chaotic melee, these rules reward precise understanding.
Definition and scope
An opportunity attack is a special melee attack that one creature makes against another creature that leaves its reach without using specific movement exceptions. The rule is defined in the Player's Handbook (Chapter 9: Combat) and applies to all creatures in the game — player characters, monsters, and NPCs alike — not just martial classes.
The scope is deliberately narrow. Opportunity attacks don't fire on every aggressive action; they exist specifically to model the real danger of turning your back on an armed opponent. A fighter who pivots and runs creates an opening. A rogue who steps back while maintaining eye contact and using the Disengage action does not. That distinction — how movement and action economy interact — is what makes opportunity attacks a genuine tactical consideration rather than a bookkeeping tax.
How it works
The mechanical sequence is short but worth walking through precisely, because the timing matters:
- Trigger: A creature that the attacker can see moves out of the attacker's reach.
- Reaction: The attacker uses their reaction to declare an opportunity attack.
- Attack: The attacker makes one melee attack against the triggering creature.
- Resolution: The attack resolves normally — roll to hit against Armor Class, apply damage on a hit.
Three details in step 1 carry enormous weight. First, the word moves — the creature must use its own movement. Being forcibly moved (shoved, thrown, teleported) does not trigger an opportunity attack unless a specific feature says otherwise. Second, out of reach — a creature that starts outside reach and stays outside reach triggers nothing; the attack fires only the moment a creature exits the attacker's reach zone during its movement. Third, can see — a blinded attacker or an invisible creature moving away generates no opportunity attack.
The reaction cost is the hidden constraint. A creature has only 1 reaction per round, reset at the start of its turn. Using a reaction on an opportunity attack means no Shield spell, no Counterspell, no readied action trigger for the rest of that round. That cost is easy to ignore until the moment a fireball goes off and the fighter's reaction is already spent on a goblin who got away with 3 hit points.
Common scenarios
Fleeing combat: The most common trigger. A creature under pressure moves away to seek cover, disengage from a losing fight, or reach a more vulnerable target. Every foot of movement that exits an enemy's reach invites the attack.
Repositioning: A player character moves from one enemy to another — for example, walking from an orc on the north side of a room to a mage on the south side — passes through reach zones along the way. Each creature whose reach is exited gets one opportunity attack. A 30-foot move through a packed room could theoretically provoke 4 or 5 attacks.
The Disengage contrast: Using the Disengage action (or Cunning Action for rogues) prevents opportunity attacks for the entire turn. This is the primary mechanical counterweight to the rule. A rogue who Disengages moves freely; a fighter trying to cross the same space does not.
Forced movement: A creature pushed by the thunderwave spell, moved by a telekinesis effect, or shunted through a misty step does not trigger opportunity attacks. The trigger is voluntary movement. This is a point worth flagging in the DnD frequently asked questions because it surprises players regularly.
Reach weapons: A creature wielding a glaive or pike has a 10-foot reach instead of the standard 5. A creature that steps from 10 feet to 15 feet away — still at a distance most weapons can't threaten — exits that reach zone and triggers an opportunity attack. This asymmetry makes reach weapons especially punishing for mobile opponents.
Decision boundaries
The rules as written (RAW) leave a handful of edge cases that require a Dungeon Master call. Understanding where RAW ends and DM adjudication begins helps at the table before anyone has to pause mid-combat.
Teleportation: Spells like misty step and dimension door move a creature without it passing through intervening space. No opportunity attack triggers. Contrast this with thunderstep, which also teleports the caster — same result, no trigger.
Mounted movement: A mounted rider uses the mount's movement. If the mount moves out of an enemy's reach, the enemy may target either the rider or the mount with the opportunity attack, at the attacker's choice.
Swarms and unusual shapes: Creatures occupying non-standard space sometimes generate questions about exactly when reach is "exited." The standard ruling treats the edge of a creature's space as the boundary — when any part of the creature's space exits the attacker's reach, the trigger fires.
Two creatures, simultaneous movement: Opportunity attacks interrupt movement. If a creature provokes an opportunity attack mid-move, the attack resolves before the movement continues. A killing blow from an opportunity attack stops the fleeing creature in its tracks — it doesn't finish the move postmortem.
The full mechanics overview covers how opportunity attacks interact with the broader action economy, including readied actions that mimic their timing without requiring the standard trigger.