In Australian rules football, playing fields have no fixed dimensions but at senior level are typically between 135-185 meters long and 110-155 meters wide wing to wing. The field is like the ball which is an oval shaped. In Australia, cricket grounds are often used. No more than 18 players of each team are permitted to be on the field at any time.
Up to 4 reserve players may be swapped for those on the field at any time during the game. In Australian rules, these reserve players are waiting for submission on the bench ( an area with a row of seats on the sideline). The players must only interchange through the designated interchange gate with strict penalties for too many players from one team on the field. But, in some leagues like the AFL, they have each team designate one player as a substitute who can be used to make a single permanent exchange of players during a game.