Do you know if an Opportunity Attack is coming?

[sir_argo]

You can make an opportunity attack when a hostile creature that you can see moves out of your reach.

How obvious is it that a person can or will take an opportunity attack? I have two examples that demonstrate the issue.


Example #1 - is that guy hostile to me?


A = (anti)Paladin
B = Barbarian
C = Cleric

A and C are fighting each other and are in melee. B walks into the room and sees the fight. B knows A and has a vendetta against him. B and C have never met each other. B sees an opportunity to settle his vendetta against A and so he activates his rage ability, draws his great axe, and charges in recklessly. C looks over and sees a raging, reckless barbarian charging into combat. There is the roleplaying aspect of C wondering if this barbarian is hostile to him or not. B is not necessarily friendly to C, but not necessarily an enemy either. C is a little nervous and wants to shift away from B, but stay in melee with A. Player C asks, "If I move away from C, will he get an opportunity attack?" The DM responds, "You're not sure. He's raging, eyes wild, and he's swinging that axe like a mad man."

Player C says, "Well crap. I don't want him to get an opportunity attack. I want to move away, but if he is going to take an OA, then I'd like to stay put."

Should C know if B will take an opportunity attack if he moves away? If yes, then the premise would be that you can tell a person is hostile because he's actively engaging you versus only actively engaging someone else. But if that's so, then we have another problem which I'll cover in example 2.


Example #2 - the assassin


The party is engaging a group of orcs. Unknown to the party wizard, the rogue is an assassin that was hired to kill the wizard. During the fight, the wizard and rogue are standing next to each other behind the front line. The wizard goes to move in a way that would take him out of reach of the rogue. Would the rogue be able to take an opportunity attack against the wizard as he moves away? The crux of this example is whether "hostile" means actively engaged, or if it just means willing to harm. Another variation of this example would be if it was a gargoyle instead of a rogue. The party is fighting all of those orcs, and the wizard thinks he's just standing next to a statue. The wizard states his intent to move--would the gargoyle be able to reveal himself by taking an OA as the wizard moves away?

[Unoriginal]

You never *know* if an Attack of Opportunity is coming, but you can still guess.

The point of the AoO is "if you move away from someone's reach, they get the opportunity to attack you". The book says "hostile" because a being who's not hostile to you isn't going to attack, while one who is will probably do so, but it's not a given. For example, an orc warlord might decide to not attack you when you back off from fighting him because he knows you're walking in the direction of an hidden-pit-with-spikes trap and he finds you falling down when you feel confident funnier than if you're more hurt.

In your Barbarian example, C can certainly see that B is focusing on A right now. Doesn't mean that C should be certain B won't attack them anyway, but it should be enough to guess "better get away when B is angry at A, then".

In your assassin example, the Rogue decides to be hostile to the Wizard, re

[Demonslayer666]

No, you honestly would never know for certain that an OA is coming. Even a known hostile enemy may decide to hold their reaction for something else. You can suspect it, but the decision to risk it is yours.

I would consider all non-party members as hostile in combat.

So for #1, yes, as DM, I would consider him hostile and allow them to take an OA, but like I said, C would not know until it happened. Once C moved, they could not take it back. If they ask me (as DM) if they will attack, I would likely tell them they don't know.

For #2, yes to both OAs, no, the Wizard would not know it's coming, and I'd have the attack made with advantage in both cases (unless the wizard was very wary of the rogue).


I'm assuming that you mean the rogue attacking the wizard is a party member in disguise, which makes my non-party members statement seem like it would prevent this, but I was gearing that more towards my game, where party members don't PVP. You don't have to be openly hostile to take an OA.

[Dr. Cliché]

My view is that (assuming you're aware of the enemy) you always know if your movement will provoke an attack of opportunity, but you cannot know whether the enemy will take that opportunity attack.

In terms of your specific scenarios:

1) I would tell C only that his movement will allow B an opportunity attack, should he choose to take it. He can do with that information whatever he wants. He can stay put, he can move and risk the attack, or he can disengage (or use some other means to escape - like Misty Step).

However, he is not allowed to know in advance whether B will actually take the opportunity attack.


2) I would allow the rogue to break cover by making an opportunity attack against the wizard. I might give the wizard an Insight/Perception check against the Rogue's Deception/Sleight of hand - if the Rogue wins, the wizard doesn't realise his intent and the Rogue gets Advantage on the attack.

[Tanarii]

Up to the DM how obvious a possible OA, ie the potential for triggering it, is in-universe.

But in (almost?) every game of D&D I've played with OAs (whatever they're called in the given edition), if they're possible, the creature knows in-universe the possibility exists. I can't think of any exceptions of a DM or Table ruling otherwise off the top of my head. In fact, it's almost always just assumed. It's also assumed that your character (or NPCs) know when they can't take an OA, such as being blinded or having already used their OA/reaction.

I thought about this after the recent Sentinel thread, and OAs while the text of them doesn't specifically say you're aware of the specific potential to trigger an OA, it certainly implies that characters are generally aware that they can occur due to movement. In other words, it doesn't make it absolutely clear that characters are aware they might trigger all OAs. Nor that there is any way to tell when a creature can't take an OA when the action would normally trigger one, such as having already used their OA.