Sportsmanship is honored...
What makes frisbee/flying disc sports unique within the world of sports today, is that the sport from the beginning is completely founded on sportsmanship. The basic idea is that there are no referees. It's the players who makes the judgemnt calls!

The spirit of frisbee/flying disc sports is to follow the rules, i.e. no cheating. Each participant take his/hers own responsibility, and you don't let a referee free yourself from the responsibility of following the rules.
 

The players make the line calls.
Here it wasn't too difficult... ;-)

In the team sport ultimate, which has a lot in common with basketball rules, it's the players on the field who makes the calls. If I see an opponent (or even a member of my own team) do anything illegal, I make a call.

If I'm the subject of an illegal body contact i call foul and the violation is taken care of with my getting the right to the disc.

In DDC (Double Disc Court), an event that has the same line ruling situations as for example tennis, or volleyball, it's the players themselves that gives the "out" or "in" calls, not a line referee.

This system works an all level of play, from the back yards to the world championships.

Of course there are situations where players in the heat of the game disagree on a call.

Ultimate frisbee is a fast paced team sport, where in parallell to the actual game results, the teams are also awarded fair play points for a separate "spirit of the game" tournament trophy!

It may sometimes take some discussion to make clear what really happened, and as a last resort in some tournaments there are "observers". These observers makes the final judging when players can't get to an agreement. So the observers don't make calls for every situation that arises during a game, but only if the players agree to let the observer give his point of view.

In DDC the players sometimes even ask the audience for a judgement call on some situations.

For the "normal" sport spectator this may not seem serious, but think about it: Isn't the cheating you see some soccer or ice-hockey player perform when he notices that the referee is looking the other way really a far more unserious behaviour?

A victory in one of the bigger tournaments can give the winner up to $10 000, but even on these occasions the absence of referees works really well.