The NFL rulebook is very specific about what is and isn’t allowed regarding its footballs.
The rulebook section titled “ball dimensions” states: “The ball shall be made up of an inflated (12 1/2 to 13 1/2 pounds) urethane bladder enclosed in a pebble grained, leather case (natural tan color) without corrugations of any kind. It shall have the form of a prolate spheroid and the size and weight shall be: long axis, 11 to 11 1/4 inches; long circumference, 28 to 28 1/2 inches; short circumference, 21 to 21 1/4 inches; weight, 14 to 15 ounces.”
The referee, according to the rulebook, is the sole judge as to whether the footballs comply with those specifications. The footballs remain under the supervision of the referee until they are delivered to the ball attendant before the start of the game.
Section 2 of the rulebook involves the supply of the footballs: “Each team will make 12 primary balls available for testing by the referee two hours and 15 minutes prior to the starting time of
the game to meet League requirements. The home team will also make 12 backup balls available for testing in all stadiums. In addition, the visitors, at their discretion, may bring 12 backup balls to be tested by the Referee for games held in outdoor stadiums. For all games, eight new footballs, sealed in a special box and shipped by the manufacturer to the Referee, will be opened in the officials’ locker room two hours and 15 minutes prior to the starting time of the game. These balls are to be specially marked by the Referee and used exclusively for the kicking game.”
The final paragraph of the rule on game balls notes that it is the responsibility of the home team to furnish playable balls at all times by attendants from either side of the playing field.