The game is essentially a grown-up version of piggy-in-the-middle, with the aim for most players being to hit the person in the middle of the circle with a frisbee (they must throw it - walking up to the person and hitting them with a frisbee you're holding is just not on).
By convention the players forming the circle keep roughly in position, or move around in a way such that the circle keeps approximately the same size throughout play.
As a concession to health and safety a hit must be above the knee and below the head. (There is no guarantee that you won't get hit below the knee or on the head.) In order to allow the middle person to fend off attacks, hits on the arm only count between the elbow and shoulder.
If you manage to land a successful hit on the middle person you get to nominate another player to take their place.
If you are in the middle and manage to hit any other player (subject to the above rules) then they take your place in the middle.
To speed the game up you may only hold on to a frisbee for a maximum of three seconds.
In order to play you will need frisbees (about 4 if there are six people). It may also be advisable to have a packet of plasters, antiseptic cream and Deep Heat available.
Very little has been written about the tactical nuances of this game.
One favourite tactic is for the players in the circle to pass the frisbee among themselves, getting the frisbees into a position from which they can launch a simultaneous, multi-directional attack on the middle player.
Some people also go for 'stacking' where a small frisbee is held under a larger one and both thrown together at the middle player.