I recently had this come up in a campaign and I know I read about it in a book somewhere but I can't find it... I had one player (a monk) that wanted to punch a chest to see if he could break it open, another player (a rogue) who thought it was trapped wanted to stop the monk player before he could trigger the supposed trap. As action technically happens simultaneously I ruled that both players should make an initiative check. The rogue attempting to grab the arm of the monk and stop him from punching the chest won the initiative check, so i ruled he had to make a touch attack to grab the other players arm. Is there a ruling somewhere in regards to this?
Here's a very simple way to handle this contest: an opposed Strength check.
The rules don't require an attack to break a chest open, d20 SRD (under Breaking Items), so the monk can make a Strength check to burst it open.
When a character tries to break something with sudden force rather than by dealing damage, use a Strength check (rather than an attack roll and damage roll, as with the sunder special attack) to see whether he or she succeeds.
Given that he's trying to muscle it open, rather than doing a super complicated opposed grapple, and given that the other player said he wants his PC to grab the monk's arm, it sounds like an opposed Strength check to me. Even simpler would be to add a +2 circumstance bonus to the break DC from the rogue's interference and be done with it!
If it were me I'd only break out the grapple rules of it was a really significant event, like the monk trying to throw a Ring of Power back whence it came and the Rogue being all "I hates monkses forever!"
If you want to stop a character from attacking, you need to use a grapple. The grapple rules are pretty complicated; the summary is that the monk can't punch anything (other than the rogue) while grappled, but grappling the monk is hard to do and hard to maintain, so if the monk really wants to punch the chest he'll eventually be able to do it.
Just for fun, here's what I remember of the grapple rules:
- First the rogue has to win initiative.
- Then the rogue has to succeed on a melee touch attack against the monk. Normally this would provoke an attack of opportunity from the monk, but if the rogue won initiative and it's the first round of combat then the monk is flat-footed.
- Then the rogue has to succeed on an opposed grapple check against the monk. If the rogue fails the opposed grapple check (or either of the checks prior to it) then the monk is not grappled and is free to act on his turn.
- On the monk's turn, he can make opposed grapple checks to escape the grapple. A grapple check doesn't use up a whole turn -- it's just an attack action. If the monk does a flurry of blows, he can use the first attack to break free, and if that succeeds he can use the second attack to punch the chest.
- If the rogue gets an action and the monk is grappled, the rogue can succeed on another grapple check to pin the monk.
- If the monk gets an action when he is pinned, he can succeed on a grapple check to stop being pinned (and go back to being grappled).
It's not clear what happens next. In 3.5, as far as I can tell, they just keep making grapple checks at each other until the rogue loses and the monk punches the chest. In pathfinder they added an option where, if the monk is pinned and the rogue has a rope, he can tie up the monk by making a CMB roll at a -10 penalty.
But monks are better at grappling than rogues (they usually have higher strength and more attacks), so it's unlikely that the rogue will win even one grapple check. If the monk wants to punch the chest, the monk is going to punch the chest.
Let me editorialize for a minute here. If two players really can't agree on what to do next, I don't think it's a good solution to have their characters fight. Letting characters fight each other leads to weird incentives -- you'll get a party full of hulking barbarians ready to fly into a rage and kill their allies if they don't obey. That's no fun for anybody.
In my games, when my players can't agree, what I do is I call for a party vote.
Moving into combat with initiative and grappling or actual attacks is one method. Having the players talk it out as a group is another. But a third and IMHO a good option is to role-play the characters! Add a little color; a little dialogue.
Encourage your players to have their characters talk to each other. Rather than every character's action being sudden and isolated, encourage them to telegraph their actions a bit when working within the group. Let's see how that might look in the scenario you've described:
Your monk's player says they want to punch it open; your rogue's player says it might be trapped so they want to stop him. If you stop them and frame that exchange first as a conversation between the characters, it gives them all more opportunities to take different approaches and think about what how their characters would interact, rather than just react.
The monk mutters, "You know, I bet I could break that open with the right punch..." and moves toward the chest. The rogue grabs his arm and snaps, "What if there's a trap?" At this point the characters have the option to argue about it, or they can of course proceed directly to initiative and trading blows or trying to restrain each other. Those same original options are still on the table, but one of your jobs as DM is to frame the environment in ways that give them as many opportunities as possible to do something interesting.
And just to be clear, you don't have to be a "Forsooth" and "Verily" LARP player to have character dialogue. Statements like: "My rogue says something like ..." and "My monk disagrees and says he's being paranoid." works just fine.