Football balls

In North America, the term football refers to a ball made of leather, which is required in professional and collegiate football. Footballs used in recreation, and in organised 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). 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. Historically, white footballs have been used in football games played at night so that the ball can be seen more easily; however, this practice is no longer commonplace, as artificial lighting conditions have improved to the point where it is no longer necessary. Two indoor American football leagues, the Ultimate Indoor Football League and American Indoor Football, use a ball with red, white and blue panels. At most levels of play (but not, notably, the NFL), white stripes are painted on each end of the ball, halfway around the circumference, to improve nighttime visibility. The UFL uses a ball with lime-green stripes. In the CFL the stripes traverse the entire circumference of the ball. The XFL used a novel color pattern, a black ball with red curved lines in lieu of stripes, for its footballs; this design was redone in a tan and navy color scheme for the Arena Football League in 2003. A leather football used in a 1932 college football game 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 for weight and blemishes, workers begin the actual manufacturing process. Typical modern American football as used in the NFL 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 to 13.5 pounds per square inch (86 to 93 kilopascals). The ball weighs 14 to 15 ounces (400 to 430 grams). In an NFL game, the home club must have 36 balls for an outdoor game or 24 for an indoor game, and they must be available for the referee to test with a pressure gauge two hours before the game. Twelve new footballs, sealed in a special box and shipped by the manufacturer, are opened in the officials’ locker room two hours before the game. These balls are specially marked with the letter "K" and used exclusively for the kicking game