FOOTBALL, AMERICAN

game played between two 11-member teams on a rectangular field with goalposts at each end. Each team tries to score points by moving the ball, which is oval-shaped, over the opponent's goal line for a touchdown (by carrying or passing the ball to a teammate) or by kicking it between the goalposts (a field goal). A team must advance the ball 10 yards in four attempts, called downs. As the possession of the ball changes from side to side, defensive and offensive teams alternate positions on the field. American-style football is a body-contact sport of running, kicking, and passing. The gridiron sport, as it is called because of the field's design, is indigenous to the United States and has not been taken up in the rest of the world to the degree that other U.S. sports, such as basketball and baseball, have. It has spread to some other countries, however, and has achieved a degree of international popularity through television viewing. American football evolved as the product of the imagination of early players and coaches who continuously adapted the game to the equipment, the players' skills, and the playing rules in effect during their time. It was coaches such as Walter Camp, Amos Alonzo Stagg, Glenn (Pop) Warner, Bob Zuppke, Knute Rockne, Robert Neyland, Don Faurot, and Herbert (Fritz) Crisler who developed the fundamentals of play and generated public interest in football. The game began as a college sport that was played in the fall and was usually over by Thanksgiving. Today, colleges have a limited practice of about three weeks in the spring, begin their fall schedule in late August, and continue through the New Year holiday with National Collegiate Athletic Association (NCAA) divisional championships and bowl games. The professional teams play exhibition games in July and continue their season through the Super Bowl in the last week of January. High school teams play shorter schedules that often lead to city and state championship tournaments. Additional reading Authoritative treatments of the early game include Allison Danzig, The History of American Football: Its Great Teams, Players, and Coaches (1956), and Oh, How They Played the Game (1971); and Forest Evashevski and David M. Nelson, Scoring Power with the Winged T Offense (1957). David L. Porter (ed.), Biographical Dictionary of American Sports: Football (1987), contains a wealth of historical information. See also John McCallum and Charles H. Pearson, College Football U.S.A., 18691972: Official Book of the National Football Foundation (1972); Robert Baldwin, College Football Records: 18691984 (1987); and NCAA Football Records (annual). Professional football is informatively presented in Harold Claassen, The History of Professional Football (1963); Beau Riffenburgh (ed.), The Official NFL Encyclopedia, new rev. ed. (1986); Roger Treat, The Encyclopedia of Football, 16th ed. (1979); David S. Neft, Richard M. Cohen, and Jordan A. Deutsch, The Sports Encyclopedia: Pro Football: The Modern Era, 1960 to the Present, rev. ed. (1987); and The Sporting News National Football Guide (annual). For the rules and organization of the game, see David M. Nelson, Football: Principles and Play (1962), and Illustrated Football Rules (1976). The National Collegiate Athletic Association publishes useful annuals, including NCAA Football, a general guide, and NCAA Football Rules and Interpretations. David M. Nelson Play of the game Rules for college, professional, and high school football are fundamentally the same; the most notable differences are pointed out in the following discussion. Field of play and equipment Figure 2: Football field according to NCAA specifications. Professional field varies slightly. U.S. football is played on a field measuring 100 yards (91 metres) in length from goal line to goal line, with an end zone 10 yards in depth behind each goal line, and 160 feet in width (Figure 2). Goalposts 23 feet 4 inches apart18 feet 6 inches apart in the NFLare erected on each end line, the limit of the end zone. A connecting crossbar is 10 feet above the ground. Parallel lines the width of the field are marked five yards apart between goal lines. An inbounds line the length of the field is marked 53 feet 4 inches inside each side line70 feet 9 inches in the NFL. The ball has the shape of a prolate spheroid. A leather case covers a rubber bladder inflated to the pressure of 12 1/2 to 13 1/2 pounds (0.780.94 kilograms per square centimetre). Its long axis measures 10 7/8 to 11 7/16 inches (27.62 to 29.05 centimetres); its short circumference measures 20 3/4 to 21 1/4 inches; and its weight is from 14 to 15 ounces (400 to 425 grams). A rubber-covered ball may be used by NCAA and High School Federation teams. The mandatory equipment for college and high school players includes head protectors, shoulder pads, hip pads, thigh guards, mouthguards, jerseys with numbers, and soft knee pads covered by pants. Other equipment, including shoes, knee braces, gloves, and injury pads, is worn but not required. The NFL has less stringent requirements for much mandatory equipment.