<P> A football is a ball inflated with air that is used to play one of the various sports known as football . In these games, with some exceptions, goals or points are scored only when the ball enters one of two designated goal - scoring areas; football games involve the two teams each trying to move the ball in opposite directions along the field of play . </P> <P> The first balls were made of natural materials, such as an inflated pig bladder, later put inside a leather cover, which has given rise to the American slang - term "pigskin". Modern balls are designed by teams of engineers to exacting specifications, with rubber or plastic bladders, and often with plastic covers . Various leagues and games use different balls, though they all have one of the following basic shapes: </P>

What is the name of the ball used in american football
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