A football game is played between two teams of 11 players each.[28][29][30] Playing with more on the field is punishable by a penalty.[28][31][32] Teams may substitute any number of their players between downs;[33][34][35] this "platoon" system replaced the original system, which featured limited substitution rules, and has resulted in teams utilizing specialized offensive, defensive and special teams squads.[36]
Individual players in a football game must be designated with a uniform number between 1 and 99. NFL teams are required to number their players by a league-approved numbering system, and any exceptions must be approved by the Commissioner.[28] NCAA and NFHS teams are "strongly advised" to number their offensive players according to a league-suggested numbering scheme