Unlike the balls used in most sports, a football is not spherical in shape so there is more of an unpredictability in the way it bounces. When thrown, ideally the ball leaves the hand spinning in a spiral motion, which keeps the flight of the ball more aerodynamic.
There are different sizes of footballs, with smaller versions available for youth play. At the NFL level, the ball measures from 20 3/4 to 21 1/4 inches around its middle, 28 to 28 1/2 inches around its ends, and 11 to 11 1/4 inches from tip to tip. It also weighs between 14-15 ounces and is inflated between 12 1/2 and 13 1/2 pounds per square inch.
When football was in its infancy, a pig's bladder was often inflated and used as the ball.