Derived from soccer and rugby in the mid-1800s, American football has grown to be the most popular sport in the United States. According to the National Federation of State High School Associations, it has the highest participation in high school sports with over one million players. Many colleges and universities feature a football program, and the National Football League is the most popular professional sport in the country.
In addition to the traditional 11-a-side outdoor game, there are several other varieties of football. Flag football is a common variation that replaces tackling with removable flags on each player that determine when the ball-carrier is down and ends the play. Similarly, touch football uses the practice of touching an opponent in lieu of tackles to end play.
Another version of the game is indoor football. Indoor football was devised in the 1980s using indoor soccer as the inspiration. Like indoor soccer, an indoor football field is typically played on a turf field the same size as a hockey rink and is 50 yards long from end zone to end zone. Indoor football features a maximum of eight field players per side. Like outdoor football, touch and flag can also be played indoors.
Indoor and arena football is played by many organized leagues across the United States at the professional and semi-pro levels. Founded in 1987, the Arena Football League is the most prominent pro league, which uses rebound netting in the end zones and dasher boards along the sidelines.