How many players from each team are on the field at once in American football?

How to get close to this number

Eleven again, the same as football and cricket, and for the same reason: it is roughly what a large outdoor field needs. When three sports with nothing else in common converge on the same number, the constraint is the pitch rather than the game.

The roster figure in the explanation is the genuinely distinctive part: up to fifty-three on an active roster for eleven on the field at a time. Offence, defence and special teams are almost entirely separate squads that substitute freely, so a team is really three teams sharing a name and a stadium.

That structure is why the sport is so specialised. A player may be on the field for a quarter of the snaps and train exclusively for one situation, which produces body types and skill sets that would be useless in any other sport. Free substitution is the single rule that shapes almost everything else about how the game is played.