Can an Opportunity Action trigger another person's opportunity action?

[ButcherMagnus]

Can an opportunity action trigger another person's opportunity action?

I've seen the rule with my own eyes (can't think of where) that says an immediate action can't be triggered by another immediate action, but is there any explicit rule that bans taking an opportunity action as a result of someone else's opportunity action? If so, where is that rule?

The example that has come up is that we have a Knight and a Slayer attempting to work in tandem. Knight is adjacent to Enemy (who is therefore is defender aura). Slayer is adjacent to the same Enemy, and moves away from the enemy on Slayer's turn. Enemy gets an opportunity attack on Slayer. If Enemy takes that attack, Enemy is within Knight's aura and because he is attacking an enemy besides the Knight, is subject to a -2 attack penalty--but is enemy ALSO subject to the Knight's at-will opportunity attack power (forget name, 1st level class ability)?

Any help greatly appreciated. Thanks.

 

[Ryujin]

One of the oldest trick in the books involves a ranged striker using a ranged attack, when adjacent to an enemy, when a defender is next to that enemy and has him marked. The enemy has to choose whether to swing at the ranged striker, risking having the defender take a good whack at him or whether he should ignore the striker, who will do him some good damage. It's legitimate, unless the rules have changed significantly with the relaesa of Essentials.

What isn't permitted is for a character to use an immediate action of his own, on his own turn.

 

[Mirtek]

Can an opportunity action trigger another person's opportunity action?

Yes

I've seen the rule with my own eyes (can't think of where) that says an immediate action can't be triggered by another immediate action,

I am not aware of such an rule. However you can't take an immediate action on your own turn, thus the opportunity for an immediate to trigger another immediate are quite rare.

 

[Mapache]

One of the oldest trick in the books involves a ranged striker using a ranged attack, when adjacent to an enemy, when a defender is next to that enemy and has him marked. The enemy has to choose whether to swing at the ranged striker, risking having the defender take a good whack at him or whether he should ignore the striker, who will do him some good damage. It's legitimate, unless the rules have changed significantly with the release of Essentials.

That's still legit.

The big change is that readying an action that would provoke an OA also provokes an OA when you ready it, in addition to when it goes off. This is intended to keep you from trying to ready an action that would provoke for use on an opponent's turn in order to avoid provoking from that opponent.

 

[Ryujin]

That's still legit.

The big change is that readying an action that would provoke an OA also provokes an OA when you ready it, in addition to when it goes off. This is intended to keep you from trying to ready an action that would provoke for use on an opponent's turn in order to avoid provoking from that opponent.

If anyone had ever tried something that rules-lawyerish when I was DMing, I'd have just had his target whack him in the head anyway.

 

[AbdulAlhazred]

That's still legit.

The big change is that readying an action that would provoke an OA also provokes an OA when you ready it, in addition to when it goes off. This is intended to keep you from trying to ready an action that would provoke for use on an opponent's turn in order to avoid provoking from that opponent.

Heh, I didn't catch that one, buy yeah, you can generate OAs with OAs or immediates, etc. as long as all use frequency and turn restrictions are met.

 

[Aegeri]

If anyone had ever tried something that rules-lawyerish when I was DMing, I'd have just had his target whack him in the head anyway.

Well now it doesn't matter, because that's precisely how the rules work to begin with.

 

[Mengu]

Sometimes there are so many triggers we forget whose turn it is.

Rogue moves to get a flank, provoking from enemy. But before that, fighter gets his combat challenge attack, hitting target. Target continues with opportunity attack and hits the rogue but the ranger will have none of that, so he takes a disruptive strike. That bloodies the enemy who has a free action that attacks everyone around him, hits the fighter and crits the rogue who are both pushed 1 square and knocked prone. The shaman uses an interrupt to take half the damage from the rogue's crit. The ranger uses the quick property daily from his bow to try and finish off the enemy but misses. Uses elven accuracy to reroll and hits. He uses Blessing of Corellon to allow the fighter to spend a surge. The fighter uses his amulet of life to spend 2.

So all of that happened during an opportunity attack. By this time, it's not unusual for the rogue to be sitting there with a glazed look on his face waiting for the ranger or the fighter to finish their turn. It's like a round of actions that happen during an opportunity action. Fortunately we use an initiative board and can prod the rogue along to take the rest of his turn.

In summary, yes triggered actions can and do trigger other actions all the time. One needs to carefully observe and make sure no one is taking immediate actions during their turn (like the rogue couldn't use halfling second chance during his turn to have the crit rerolled), and make sure no one is taking multiple immediate actions in one round (like the fighter couldn't use Hold Your Ground utility to not be pushed because he already used Combat Challenge attack as his immediate action). And have to make sure no one is taking multiple free action attacks during the turn (like the monster couldn't use it's Rampage free attack when it critted because the crit happened for a free attack during this turn).

 

[ButcherMagnus]

Many thanks to all! That definitely clarified things for me! Also, having looked through the rules again, it appears that the passage I saw "with my own eyes" was seen, but not understood at all. This is why I should not be a witness. There is indeed no rule which states that any triggered action (immediate or opportunity) cannot be triggered by another triggered action (immediate or opportunity), subject of course to the rules you cited above, and the limit on immediate actions to one per turn. I appreciate it.

 

[Aegeri]

Rogue moves to get a flank, provoking from enemy. But before that, fighter gets his combat challenge attack, hitting target. Target continues with opportunity attack and hits the rogue but the ranger will have none of that, so he takes a disruptive strike. That bloodies the enemy who has a free action that attacks everyone around him, hits the fighter and crits the rogue who are both pushed 1 square and knocked prone. The shaman uses an interrupt to take half the damage from the rogue's crit. The ranger uses the quick property daily from his bow to try and finish off the enemy but misses. Uses elven accuracy to reroll and hits. He uses Blessing of Corellon to allow the fighter to spend a surge. The fighter uses his amulet of life to spend 2.

That is so epic.

My best was something like this, caused by the Barbarian being on 11ish HP. Too tempting a target, even when marked.

Initial action: A balor used a power to attack the Barbarian. The balor is marked.

Fighter>Opportunity Action: Fighter attacks the Balor - Warpriest Mark. Hit's easily.

Fighter>Immediate Interrupt: Fighter attacks the balor - Combat Superiority. Misses. Rolls a 1.

Fighter>Rerolls the 1, misses entirely.

Balor attacks and misses the barbarian.

Balor>Daemonic accuracy. Hits the Barbarian and drops him.

Cleric>Immediate Reaction: Uses healing word and the Barbarian gets back up.

Balor>Soul Stealer (Free action attack when an enemy within the aura spends a surge). The Balor thumps the Barbarian immediately for spending a surge, almost downing him again.

Barbarian>Some power (can't remember): Made a melee attack against the balor for attacking him, hitting and bloodying the balor. It's also a critical hit.

Barbarian>Rampage attack (Free action). Misses the Balor though.

Balor>Flaming Burst (My own power, triggers on bloodied, no action). Targets the cleric, barbarian and fighter with a burst attack, hitting all three targets.

So that was a whole lot of actions for just one attack

The Barbarian did end up unconscious at the end of it incidentally.