How should this situation play out?

[Kurotowa]

Tsk, I didn't realise I was opening up a can of worms.

Actually, the simplest solution is to have a DM who won't sweat the details. Then the players just say, "We throw the door open, toss in a fireball, and jump them while they're surprised and crispy." And the DM says, "Okay, roll the fireball damage and tell me what you're doing with your surprise round." Because that's what the players what to get done, and doesn't worry about timing and held and readied actions.

But, since this is the Rules forum and a rules question, that's not as helpful. I suppose the real question is if the door opening+fireball is the trigger for starting the surprise round or happens during the surprise round.

 

[Elder-Basilisk]

Hmmm. It sounds to me like the "don't sweat the details DM" just asked to get two fireballs tossed into the room during the surprise round.

DM: You toss the door open and fireball them. Now you get a surprise round.
Sorcerer: Sweet, I fireball them again.

Things like that are why details are important. I guarantee you that 99% of players would sweat the details if it happened to them.

 

[atom crash]

I had a situation where the party infiltrating a hobgoblin stronghold listened at a door and heard movement and grunting/talking on the other side. Since they were in a hobgoblin stronghold, they were pretty sure there were hobgoblins on the other side of the door. The plan was to open the door, toss a fireball in, then slam the door closed. The problem? The room was smaller than the blast area of the spell. I allowed them to make a reflex save to get the door closed in time to avoid backblast.

If I had to do it again, I probably wouldn't handle it that way. It would easily become the preferred modus operandi (the PCs have a wand of fireballs with 20-something charges left). Luckily for me, the reflex save was failed, the door was not closed in time, and the fireball cooked two party members (the sorc/rogue with the wand and the dwarf who opened the door) as well as the room full of hobgoblins. They don't try that trick anymore.

But then again, their standard operating procedure is for the dwarf to kick in the door and everyone else rush in. When the dwarf kicks in the door, everyone rolls initiative and the dwarf invariably goes last. He's standing in the doorway, right in everyone's way. So there is no charging, and the surprise round usually ends with everyone having moved but noone getting to attack. Obviously they're looking for a new tactic.

 

[moritheil]

Exactly. The DM declares when combat begins (and ends); not the players. Otherwise you get these situations where players try for two surprise rounds.

Hmmm. It sounds to me like the "don't sweat the details DM" just asked to get two fireballs tossed into the room during the surprise round.

DM: You toss the door open and fireball them. Now you get a surprise round.
Sorcerer: Sweet, I fireball them again.

Things like that are why details are important. I guarantee you that 99% of players would sweat the details if it happened to them.