Polyvinyl chloride or leather laces are inserted through the perforations, to provide a grip for holding, hiking and passing the football. Before play, according to the NFL rules, the ball must be inflated to an air pressure between 12.5 and 13.5 pounds per square inch (86 and 93 kilopascals).
American football evolved from two games that were popular in other parts of the world: soccer and rugby. In 1880, Camp authored rules that reduced the number of players per team from 15 to 11 (today’s total) and replaced the rugby scrum with the center snap to put the ball in play.
Among these important changes were the introduction of the line of scrimmage, of down-and-distance rules, and of the legalization of forward pass and blocking. In the late 19th and early 20th centuries, gameplay developments by college coaches such as Eddie Cochems, Amos Alonzo Stagg, Parke H.