So, question, when you get a free attack from style feats, like snake fang or panther style, they allow you to "make an unarmed strike against that opponent". Can this unarmed strike be used for a combat maneuver (like trip, disarm, or grapple) or does it have to be to deal damage? I suspect it is safe to use crane riposte for this, it just lets you take an attack of opportunity but does not call out "unarmed strike" specifically, but for the others I am not so sure. For panther style in particular, if upgraded with panther parry, it could lead to some interesting situations where an opponent was tripped or disarmed before the triggering attack lands...
No, it must specifically be an Unarmed Strike which is a specific type of "weapon". Also to clarify, grapple would not be an option because it requires a standard action to perform. It cannot be done in place of a regular melee attack, only trip, disarm, and sunder can.
Yes, there are specific feats and weapons that allow for their use during combat maneuvers that aren't trip/disarm/sunder and they are specific exceptions to the general rule they maneuvers outside of trip/disarm/sunder don't use weapons. Specific always trumps general.
But as you noted, Snake Fang and Panther Style both specifically state Unarmed Strike, not just an attack. So you must make an unarmed strike, nothing else.
Edit: Also you still can't make a grapple as something other than a standard action (except maybe with feats) as I stated originally. Having a weapon like a dan bong (which causes you to take a penalty to grappling for not having both hands free netting you a negative bonus) just means you can use the weapon when performing the grapple.
Pretty much Claxon has it. Where the feat says you get "an unarmed strike" then that's what you get. Unarmed strike is a specific form of unarmed attack on it's own, like a specific weapon attack. If the description said "an unarmed attack" then a maneuver performed unarmed would be acceptable, because a maneuver is another form of unarmed attack than an unarmed strike, but it doesn't say that.
For example, Crane Riposte specifies "an attack of opportunity" which means you can make any kind of attack you could make as an AoO, be it armed, unarmed, maneuver, etc.
Pretty much Claxon has it. Where the feat says you get "an unarmed strike" then that's what you get. Unarmed strike is a specific form of unarmed attack on it's own, like a specific weapon attack. If the description said "an unarmed attack" then a maneuver performed unarmed would be acceptable, because a maneuver is another form of unarmed attack than an unarmed strike, but it doesn't say that.
For example, Crane Riposte specifies "an attack of opportunity" which means you can make any kind of attack you could make as an AoO, be it armed, unarmed, maneuver, etc.
I am not sure I understand. "unarmed strike" seems to just be what they call the default unarmed attack. If it instead said, "you may make a flail attack"...or for that matter "an unarmed strike _attack_" would you be able to make a trip then?
(And don't get me wrong, my gut instinct was that it doesn't work, but I can't quite get my head around why.)
Also, Calaxon, thanks, I did miss that grapples worked a bit differently, that clearly will not work now that you pointed that out.
EDIT: Hmm, I guess "unarmed strike" is less generic than I thought. I just stumbled across the Feral Combat Training feat in the FAQ that lets you use other natural attacks in place of unarmed strikes, although the question on the hypothetical flail version still stands.
Flail attack would mean an attack with a flail, not a combat maneuver with a flail. If it instead said attack or melee attack that is generic and per combat maneuvers:
When performing a combat maneuver, you must use an action appropriate to the maneuver you are attempting to perform. While many combat maneuvers can be performed as part of an attack action, full-attack action, or attack of opportunity (in place of a melee attack), others require a specific action. Unless otherwise noted, performing a combat maneuver provokes an attack of opportunity from the target of the maneuver. If you are hit by the target, you take the damage normally and apply that amount as a penalty to the attack roll to perform the maneuver. If your target is immobilized, unconscious, or otherwise incapacitated, your maneuver automatically succeeds (treat as if you rolled a natural 20 on the attack roll). If your target is stunned, you receive a +4 bonus on your attack roll to perform a combat maneuver against it.
Maneuvers besides trip, disarm, sunder are all standard actions to perform.