In multiplayer games, the other players often become additional features of gameplay, possibly being valuable allies or challenging obstacles. Relationships between players can be uncertain and, usually, degrade into enmity through deception and betrayal. However, depending on the game, the dynamics of relationships can vary greatly, just as the way in which they break into betrayal. Betrayal is typically viewed as a negative and anti-social interaction, but it is also capable of providing memorable experiences of gameplay. Indeed, many games not only allow betrayal but encourage it, and provide means for it to happen. In some cases, it is designed, and in others it manifests emergently and entirely a social phenomenon external to the game. This study analyses the different forms of betrayal in multiplayer games and how they manifest in gameplay and proposes a conceptual model of betrayal in multiplayer games, capable of describing its process and of analysing it formally. With the theoretical basis of this model, it is expected that it can aid in structuring betrayal mechanics and dynamics in game design.