In North America, the term football refers to a ball which is used to play American football or Canadian football. Nearly a prolate spheroid, it is slightly pointed at the ends, unlike the more elliptical rugby ball. The ball is about 11 inches (28 cm) long and about 22 inches (56 cm) in circumference at the center. The exterior of the ball is made of leather, which is required in professional and collegiate football. Footballs used in recreation may be made of rubber or plastic materials. Leather panels are usually tanned to a natural brown color, which is usually required in professional leagues and collegiate play. At least one manufacturer uses leather that has been tanned to provide a "tacky" grip in dry or wet conditions. The leather is usually stamped with a pebble-grain texture to help players grip the ball. Some or all of the panels may be stamped with the manufacturer's name, league or conference logos, signatures, and other markings. Four panels or pieces of leather or plastic are required for each football. After a series of quality control inspections to for weight and blemishes, workers begin the actual manufacturing process. Two of the panels are perforated along adjoining edges, so that they can be laced together. One of these lacing panels receives an additional perforation and reinforcements in its center, to hold the inflation valve. Each panel is attached to an interior lining. The four panels are then stitched together in an "inside-out" manner. The edges with the lacing holes, however, are not stitched together. The ball is then turned right side out by pushing the panels through the lacing hole. A polyurethane or rubber lining called a bladder is then inserted through the lacing hole. Polyvinyl chloride or leather laces are inserted through the perforations, to provide a grip for holding, hiking and passing the football. Before play, the ball is inflated to an air pressure of 12.5–13.5 psi (86–93 kPa). The ball weighs 14–15 ounces (397–425 g). Regardless of the material used in manufacturing, the ball is sometimes colloquially referred to as a pigskin. http://en.wikipedia.org/wiki/Image:Wilson_American_football.jpg Also: Digest of Rules Ball 1. The home club shall have 36 balls for outdoor games and 24 for indoor games available for testing with a pressure gauge by the referee two hours prior to the starting time of the game to meet with League requirements. Twelve (12) new footballs, sealed in a special box and shipped by the manufacturer, will be opened in the officials’ locker room two hours prior to the starting time of the game. These balls are to be specially marked with the letter "k" and used exclusively for the kicking game.