Ultimate is the most widely spread of all flying disc sports. It is played with teams of seven-on-the-field on a grass field which is approximately the size of a football pitch. The number of substitute players is not restricted, but the minimum team roster at WUGC is 12 players. In terms of tactics, the sport bears similarities to American football, but is played with a continuous and faster pace, much like soccer or rugby. Physical contact, however, is not allowed. A goal is scored by catching the disc in the end zone. A major difference to other sports is that the players act as referees themselves on all levels of competition, including the World Championships.