Attacks of Opportunity (or Opportunity Attacks in the more modern parlance) is a rule that was introduced in D&D 3.0, and has been part of Dungeons & Dragons ever since.
Older versions of the game – like Old School Essentials (OSE) and B/X – never had a rule that covered this as it was left completely up to the GM, never even considered, or handled in a different way (long weapons going first in melee combat, is an example in AD&D).
In keeping with the spirit of old school gaming, keeping it simple and fast is optimal.
A version of this article first appeared in Issue 16 of d12 Monthly. That issue is all about weapons so check it out if you are wanting more rules and inspiration regarding weapons in your D&D campaign.
What are Attacks of Opportunities (AoO)?
AoO are basically a way for attackers to get a free attack on their opponents if the opponent does something that lets their guard down.
An opportunity attack is a free attack (outside the normal action economy) made by a combatant when an occasion presents itself – their opponent is distracted, in an awkward position (climbing up a rope), moving out of combat, healing another, casting a non-attacking spell, and a few other cases (listed below).
Each combatant only gets one AoO per round.
It’s a neat little rule that can help the GM not allow characters (or monsters or enemy NPCS) from chugging down a potion in the midst of chaotic combat (which, if you think about it, makes sense).
Keeping it Simple
In keeping with the spirit of old school gaming, keeping it simple and fast is optimal.
While there is a large list of possible actions that could provoke an attack of opportunity, I would limit it to a few standard ones, and then make a call on individual cases during the game.
The key with AoO is that your opponent needs to be in reach of you to gain one.
This could be due to the two of you exchanging blows the round before or they have a reach weapon (a weapon that can reach 10-ft or more).
For example, you could rule anytime an opponent leaves combat*, stands from a prone position, or fires a ranged weapon when an attacker is in reach they provoke an opportunity attack.
Then, if a character tries to drink a potion while engaged with an orc, you may rule that the orc receives an opportunity attack against them.
Leaving it up to the GM to decide if an opportunity attack is warranted adheres to the rulings over rules spirit. Of course, you could have hard and fast rules for it as well.
Combining these two philosophies – rules and rulings – can give the players a certain level of certainty and the GM a framework to make adjudications easier and fairer.
Triggering an Opportunity Attack
For an opportunity attack to take place, the following must happen.
The Attacker is…
… aware of the opponent
… not stunned, bound, blind, or similar
… not surprised
… is within reach
And, the Opponent…
… performs an action that would distract them from an opponent
… or, moves out of combat* or past an opponent
* unless they use the whole round doing so.
An Example
Xain, our resident mage, and Tenaziir, our cautious cleric are slowly making their way down a 10-ft wide hallway in a crypt.
They can see the passage opens into a chamber up ahead, but as Tenaziir (who is in front) ducks under some ancient cobwebs, two dusty zombies burst from the walls and attack our adventurers.
Roll for surprise. Neither Xain not Tenaziir were surprised: they were seemingly prepared for anything.
Roll for side initiative. The zombies win!
One lashes out towards Xain, the other attacks Tenaziir.
The mage is hit for 5 points of damage, and the zombie on Tenaziir misses.
Having only 8 HP, Xain is battered badly and so wants to cast Shield on himself. The GM rules that as they are in such tight quarters and the zombie just struck Xain, that if the mage casts a spell – something that requires concentration – the zombie will get an attack of opportunity on him.
Xain’s player decides the risk is not worth it, and tries to retreat, spending his actions for this round, moving back down the passage to cast the spell next round.
Meanwhile, Tenaziir smashes the skull in on his zombie, dropping it to the ground.
Initiative is rolled for round 2. Zombies win again.
Intent on destroying the mage, the zombie on him turns his back on Tenaziir and shuffles towards Xain. Because the zombie has ignored Tenaziir – a combatant standing within reach of it – the cleric gets an attack of opportunity on the zombie.
He hits and destroys this one as well.
Our adventurers take a breather and continue down the passage…
Over to You
Do you like the Attacks of Opportunity rule? Can you see yourself using it in your OSE or other old school game?
While You’re Here…
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