Scenario: A character A is maintaining a grapple of another character B (who is currently stunned). The grapple has already been initiated the round before. A third character C is in melee distance of A.
During A's turn, A takes either the "Attack Your Opponent" or "Damage Your Opponent" option from the actions that can be taken while in a grapple.
Is C allowed to make a attack of opportunity on A?
I haven't found any clues in the description of grappling. Another source I found is table 8-2, “Combat Actions”, in the PHB that states for a Grapple either:
(1) Regardless of the action, if you move out of a threatened square, you usually provoke an attack of opportunity. This column indicates whether the action itself, not moving, provokes an attack of opportunity.
(7) These attack forms substitute for a melee attack, not an action. As melee attacks, they can be used once in an attack or charge action, one or more times in a full attack action, or even as an attack of opportunity.
It's seems to me that the bolded parts clash, the first granting a generic AoO and the second denying a generic AoO.
Also, others questions about grappling in almost same situation:
- C attacks A with success: does the grapple on B end? [no, in my understanding, grapple is independent from damage taken by winning grappler]
- C joins the grapple A [automatically]: how the grapple on B can end?
- Another character D performs a winning Bull Rush on A. Does the grapple on B end? [In my understanding, D is bull-rushing both of them]