Well uh... the players don't get to do any fighting themselves, they're like disembodied ghosts that control the troops. So it basically plays like a classic strategy game. A player 'dies' when the three grunts in his squad are killed. A frag is awarded every time one player's grunt takes out another player's. An additional frag is awarded if it was the last grunt on that player's squad.
It works for deathmatch and it has rudimentary teamplay support. I'm also working on a round-based "Last Man Standing" game mode.