Ultimate is played between two teams of seven players on a large rectangular field. A line drawn across the field at either end creates two “endzones” (like in American Football). These are the goal-scoring areas. A goal is scored when a team completes a pass to a player in the endzone they are attacking.
Players cannot run with the disc. When you receive the disc, you must come to a stop as soon as possible, then throw it to another player. By passing from player to player, the offense attempts to work the disc up the field towards the endzone they are attacking. If the disc hits the ground, is intercepted or is knocked down by the opposing team, then the opposing team takes possession (a change of possession is called a “turnover”, like American Football). Possession also changes if a receiver is outside the playing area when catching the disc, or if a thrower does not get rid of the disc before 7 seconds (called a “stall”).
The defending team attempts to stop the team with the disc from making progress upfield by marking them (as in soccer or basketball). The theory is that the offense is less likely to pass to a player who is being marked closely, as it increases the chance of the disc being intercepted or knocked down. The offensive players are constantly trying to get free of their markers to receive a pass, while the defense makes every effort to stay with them in the hope of forcing a turnover.