delericho
Legend
When controlling intelligent enemies who have tactical reason to achieve combat advantage (such as back-stabbing thieves or trip-attacking wolves), I have all of the enemies move into position, hold their attacks, and then unleash all of their attacks once they are flanking enemies with combat advantage.
The complaining player is arguing that I need to move Thief 1, attack with Thief 1, and then move Thief 2, attack with Thief 2, etc. I think that I should be able to coordinate attacks by delaying actions so they can deal more damage.
Hmm, interesting. My gut feeling on reading your OP was to side with the player... but then the later posts corrected that misconception. The bottom line: per the rules, you are right.
(You're also right because, as DM, it is within your remit to make appropriate rulings when running the game. But in a discussion about the rules, that's an aside.)
It's worth noting, of course, that in D&D's turn-based combat, each PC and monster has its own discrete turn that are resolved in sequence but that, in the 'real' situation that the rules are supposed to be modelling that is a nonsense. That is, on the gameboard Thief1 moves and attacks and then Thief2 moves and attacks... in a real situation, they would both move concurrently.
(I would also note that you should, of course, play monsters in a manner consistent with the intelligence/wisdom. So, having the thieves, or the wolf-pack, operate in this manner is entirely appropriate. Having a band of zombies to the same is not so appropriate. Although even then, I would argue that it is the "seeking combat advantage via flanking" that is the issue there, not the "attacking all at once" thing.)
Oh yes, one more thing: IME, players have no qualms about using the rules and/or the tactical situation to extract maximum advantage for themselves and their allies. If they can scrape up a +1 bonus from somewhere, you can bet they will, especially if that +1 bonus is the difference between a near-miss and a hit. (Unfortunately, they seem less rigorous about making sure they don't forget, or in the worst cases 'forget', every -1 penalty... Odd, that.)
That being the case, I see absolutely no reason the DM should do otherwise on behalf of the monsters. You absolutely should be fair, but in a life-or-death struggle, you should be damn sure to have your monsters fight as hard as they can to stay alive!