The National Football League (NFL) may be the top tier for American football in the United States, but its historical importance is much less significant. The sport we know today had its beginnings in the 19th century, when it diverged from the English sports of association football (soccer) and rugby football (rugby).
Many of the rules that led to American football were championed by Yale University graduate and football coach, Walter Camp. He had been a rugby player before he began to make tweaks to the game. Camp originated the line of scrimmage and the downs system that distinguish American football from other forms of the sport.