Earlier, you talked about Bob the fighter, who was
unconscious and later woke up, prone, to find Grog the orc
standing in his space. You said Bob has to stay prone so
long as he remained in Grog’s space, and that Bob would
provoke an attack of opportunity upon leaving that space.
Suppose Bob made a grapple attack on Grog? He can
grapple Grog, can’t he? Bob would be at a negative for
being prone but would not provoke an attack of
opportunity, would he? Assuming Bob establishes a hold on
Grog, how long does the prone penalty last?
Sure, Bob can grapple Grog. Bob’s initial grab attack
provokes an attack of opportunity from Grog unless Bob has
the Improved Grapple feat or some other circumstance prevents
Grog from threatening Bob. (For example, Grog would not
threaten Bob if Grog were wielding a reach weapon.) If Grog
deals damage to Bob with an attack of opportunity, Bob’s
grapple attempt is over.
If Grog doesn’t damage Bob, Bob’s initial touch attack
would suffer a –4 penalty for being prone. If the grab succeeds,
Bob is still prone and still suffers the –4 penalty for being
prone for the ensuing opposed grapple check. [...]