Attack of Opportunity - some corner cases (and specters) [closed]

Question

We had a D&D 5E session where a Specter besides a character and a wall "moved" into the wall without leaving the reach of the character, but depending on how you consider reach to work with obstacles and when you leave it, would there be an opportunity attack?

The rules on opportunity attacks state:

You can make an opportunity attack when a hostile creature that you can see moves out of your reach. To make the opportunity attack, you use your reaction to make one melee attack against the provoking creature. The attack occurs right before the creature leaves your reach.

You can avoid provoking an opportunity attack by taking the Disengage action. You also don't provoke an opportunity attack when you teleport or when someone or something moves you without using your movement, action, or reaction. For example, you don't provoke an opportunity attack if an explosion hurls you out of a foe's reach or if gravity causes you to fall past an enemy.

• So we have normal case where someone Hostile moves past the Defender, and gets hit leaving * since moved out of reach, getting opportunity attacked:

---*->H
 .D.
 ...

• Then we have case where someone moves in a circle around the defender - no opportunity attack:

---+
 .D|
 H-+

• So what if someone runs by an open door, or an alcove or something. A tunnel opening by someone with reach like a lance? Is there an opportunity attack (it feels like there should be)? Where? What about 10ft reach? Things are getting a bit weird now, but seems like there should be an attack of opportunity at one of [?]:

---???->H
===.===
 ..D..
 .....
 .....

• Ok, so what if some hostile runs a circle around someone, and there is a wall or pillar or something enough to give 100% giver temporarily? Now we have a case where hostile arguably is better off than the No Opportunity Attack circle (cover some of way), yet is arguably worse off than running across doorway (less cover yet it felt right door runner had got opportunity-attacked. Technically reach not needed if thin iron plate of right size, but for sake of ASCII art:

--?->H
 ..=..
 ..D..
 .....
 .....

• And the case that got us thinking about it all. Specter beside Defender (no reach) and a wall moves into wall. Would there be an opportunity attack? Specter did not leave reach by distance, yet is not reachable. But if there is an opportunity attack, what if specter just "fell" through floor? Falling by someone does not cause an opportunity attack? By now the whole thing just seem broken.

.-|->S
.D|
..|

Any suggestions on what RAW and (perhaps) what common sense says about these cases?

Answer 1

There are two conditions for triggering an attack of oppurtunity. Firstly

a hostile creature that you can see

Second

moves out of your reach

If it meets both of those criteria you can attack, if it does not meet both then you can not.

Your text diagrams are a bit hard for me to follow but I can understand from your description. In you example of an enemy running past a doorway I think I made a decent illustration here The enemy would trigger the attack of opportunity at this point if the player has a 10 ft. reach weapon

Now you question about the specter moving into the wall I think I made a decent illustration here. that same player would be able to opportunity attack at this point with his 10 foot weapon BUT he can not see the target therefore he does not get an opportunity attack

Answer 2

KISS it

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

... is not an ambiguous sentence. It doesn’t say when they “break your line of sight”. Nor, when they “move into the wall”. Nor, when they “dress in drag and do the hula”. Don’t put words in that aren’t there.

If they leave your reach you can make on opportunity attack. If they have total cover, that attack will miss. If they don’t leave your reach, you can’t. Even if they go from not having cover to having cover or vice-versa.