Unlike most team sports, Ultimate is self-refereed. The rules of play states: "Flying disc sports have traditionally relied upon a spirit of sportsmanship which places the responsibility of fair play on the players themselves. Highly competitive and committed play is encouraged, but never at the expense of the bond of mutual respect between players, adherence to the agreed upon rules of any event, nor the basic enjoyment of play. Protection of these vital elements serves to eliminate adverse conduct from the playing field. The responsibility for the maintenance of this spirit rests on each player's shoulders."
-  WFDF: Spirit of the Game