Have you ever wondered why there are 4 downs in American football? And just what is a down? The definition is that it’s the system by which possession is determined. The offense has four attempts (or downs) in which to make 10 yds (or more), and if they do so they keep possession.
The down is a distinguishing characteristic of the game compared to other codes of football but is synonymous with a “tackle” in rugby league. In rugby, early 19th century, when the ball carrier was stopped he would say “HELD!” and the opponent would say “HAVE IT DOWN”.
Since the ball carrier had declared himself unable to advance he would set the ball down initiating a new scrimmage. In American football, they rule the player down immediately when going to the ground or forward momentum is stopped.
The American football game was based on a combination of the Canadian rugby game and the 1874 American football game. Canadian football has three downs and different scoring points than ours. We were using 3 downs to get 5 yards but a lot of injuries and deaths were occurring.
Walter Camp changed the rule to be 3 downs to get 10 yards in 1906 which did not go over well. It became harder to get a first down and there was a huge increase in punts. In 1911 they changed it to 4 downs to get 10 yards and that has stuck ever since.