From its beginnings in the American counterculture of the late 1960s, ultimate has resisted empowering any referee with rule enforcement. Instead, it relies on the sportsmanship of players and invokes the "spirit of the game" to maintain fair play. Players call their own fouls, and dispute a foul only when they genuinely believe it did not occur. Playing without referees is the norm for league play but has been supplanted in club competition by the use of "observers" or "game advisors" to help in disputes, and the professional league employs empowered referees.