Is it possible for an attack of opportunity to provoke an
attack of opportunity? For example, a fighter attempts to
trip a cleric. The cleric chooses to make a sunder attack
against the fighter’s weapon as his attack of opportunity.
Does the sunder attack then provoke an attack of
opportunity from the fighter?
Yes. An attack of opportunity is adjudicated just like any
other attack, and it is subject to the same rules (including
provoking additional attacks of opportunity). This can lead to
odd situations where as the reason for the original action no
longer exists. If this starts to confuse you, just remember that
D&D combat is an abstract representation of battle, and not
necessarily a precise second-by-second representation of every
maneuver. Even the “sequential” nature of D&D combat—I
make my attacks, then you make your attacks, then I make my
attacks, and so forth—is an artificial creation used to keep
combat moving quickly.
Using the example you provide, the fighter is indeed
allowed to make an attack of opportunity against the cleric.
(This attack could, in turn, provoke yet another attack of
opportunity from the cleric, but the cleric could make such an
attack only if he were allowed more than one attack of
opportunity in a single round.)
These attacks are performed in a “Last In, First Out”
sequence. The last attack of opportunity declared is the first one
resolved, with the remaining attacks resolved in reverse order
of their declaration, assuming the character can still make the
attack. If the fighter drops the cleric with his attack of
opportunity, the rest of the attacks in the sequence—including
the cleric’s attack of opportunity and the fighter’s original trip
attack—do not occur. The actions are still “spent,” however—
the fighter doesn’t get to use that original attack on some other
target (although if he has other attacks remaining he may take
them as normal).
