Large scale battles take place over planets, areas, etc etc. These fights are done in something of a turn order. For instance, if the romulans are attacking a federation installation, then the romulans would post something happening, but nothing too big. The federation would have to have a chance to post in retalliation, and the romulans would also have the chance to post in offense. No consecutive posting however.

Smaller scale fights are usually done between two mercenaries or bounty hunters, or maybe a starfleet oficer and a nausiken for example. These are conducted similarly to the battles but usually have less affect on story line. 