Ultimate is predominantly self-refereed, relying on the on-field players to call their own infractions and to try their best to play within the rules of the game. It is assumed that players will not intentionally violate the rules and will be honest when discussing foul calls with opponents. This is called Spirit of the Game. After a call is made, the players should agree on an outcome, based on what they think happened and how the rules apply to that situation. If players cannot come to agreement on the call's validity, the disc can be given back to the last uncontested thrower, with play restarting as if before the disputed throw.