In one of my favorite movie firefights - in Tears of the Sun - Bruce Willis and his small team of Navy Seals are caught under heavy fire by an overwhelming opposition. They survive (well, some of them, anyway), by tactfully holding the line and then retreating. Watching this scene made me think of a combat skill that allows you to coordinate your group in battle, called "Battle Tactics".
Since combat time is based on action/reaction, a leader or other combat unit can call out a command or request (e.g. "cover me") and the recipient(s) of the command will be able to react to it, rather than have to wait until their normal turn. Naturally, the team will have to be trained in battle tactics, otherwise they will not be able to coordinate; an unskilled combatant might think, "What? What does he want me to do?".