For questions about handling game situations where players are acting in opposition to each other, rather than jointly tackling problems presented by a GM.
Player-versus-player (PvP) is a mode of play where the player characters are acting against each other, rather than jointly tackling problems presented by a GM.
This is sometimes seen as a problem, as in many traditional games, the intent is that players are united against the GM-run villains. This is compounded in many cases by the potential for hurt feelings and/or letting PvP in play bleed over outside the game.
PvP is sometimes embraced in rulesets as a viable way to play; in such cases, the GM is there to referee more than drive the plot.
In a subset of games that embrace a certain level of PvP, specific rules for PvP actions exist. Exemplar games include Houses of the Blooded, Blood and Honor, Burning Empires, and Burning Wheel.