Two Young Blonde Girls With The Football Ball On The Lawn

In North America, the term football refers to a ball used to play American football or Canadian football (both of which developed from Rugby football). It is also referred to as a "pigskin", because of their early use of pig's bladder to cover the ball.
There is much debate as to why the American football is called a "foot" ball. The primary reason is that the ball measures 12 inches (1 foot) in length. The ball is sometimes kicked forward with the foot. Another reason might be that as with association football and rugby football the game was played on foot and not on horseback, not due to using the foot to kick the ball.
Nearly a prolate spheroid, the ball is slightly pointed at the ends, unlike the more elliptical rugby ball. The purpose of this design is to make the ball the most efficient shape to facilitate the forward pass. The Canadian football is slightly less prolate than the American ball and has a closer resemblance to a rugby ball.
The ball is about 12 inches (30 centimetres) long and about 22 in (56 cm) in circumference at the center. American and Canadian footballs have different size standards, but those standards do overlap, making it possible for one ball to be used in either sport. The exterior of the ball is made of leather, which is required in professional and collegiate football. Footballs used in recreation, and in organized youth football, may be made of rubber or plastic materials (the high school football rulebooks still allow the inexpensive all-rubber footballs, though they are less common than leather).