So, let's say I'm the DM, and one of the players goes traitor, probably at a hugely inopportune time, such as when a dragon is attacking the party. Cleraly the battle became harder, and the PCs will be granted far more exp. But how much is a PC worth in combat? From what I've heard, D&D is not built for PvP (hah) combat. Is there a hard rule, or does anyone have a good idea on how to do this?