Why do nfl teams only play 16 games a season and 50 players in one roster the sport seems a little undemanding compared to say UK rugby or even the nba 82 games and mlb 100 plus games?

Answer 1

NFL teams play only sixteen games in a season because there is a much greater risk of both collision and fatigue-related injuries than in Baseball, Basketball or even Ice Hockey. Basketball and baseball are not collision sports like gridiron or ice hockey, and ice causes much less fatigue for players than the hard grass or synthetic surfaces on which gridiron football is played.

The result is that, whereas the NBA, NHL and MLB can have several games per week, this is impossible in the NFL: players would be exhausted beyond their physical capacities.

The reason for the fifty man roster is for depth on the team if there are any injuries or tired players. Eleven people are on the field at once for each team. Some players are designated to play special teams. 22 starters, maybe about 5-10 designated special teamers, a kicker & a punter make up 34 of the players right there. In basketball for contrast, you're only fielding five players at a time with a bench of about 5 more.