In both American and European football, no more than 11 players are allowed on the field at any one time from each team. In American football, teams can substitute players at will, while European soccer restricts substitutions to either three per match or a number agreed upon by both teams.
The National Football League restricts rosters to a total of 53 players, and only 46 of those can dress out for the actual game. This large number is due to the fact that offensive and defensive positions are very different and occupied by different players. European football squads generally number 25 players, and a certain percentage of those must be "homegrown" or from the region the team represents.