The NFL is very precise about its game and equipment – including the number of footballs prepared for games, how much each must weigh, and who monitors them until kickoff.

One rule is very clear: Don’t tamper with a football once it has been inspected for use in a game.

The NFL is investigating a report that the New England Patriots used under-inflated footballs in the AFC championship game while beating the Indianapolis Colts, 45-7. ESPN cited anonymous sources Tuesday night in reporting the league found that 11 of 12 balls were under-inflated by 2 pounds per square inch of air.

Here are some things to know about the issue:

CHAIN OF CUSTODY

Footballs are delivered to the officials’ dressing room 2 hours, 15 minutes before kickoff. The referee inspects each one, with a pump provided by the home team to adjust air pressure as needed.

Footballs are required to have at least 12.5 psi and no more than 13.5 psi. Releasing air can make the football easier to grip, especially when wet. Some quarterbacks prefer a softer ball to control the spin more while others like more air. A drop in temperature – from the officials’ dressing room to an outdoor field – also can cause a football to lose pressure.

THE REF RULES

The referee is the sole judge of whether a ball is fit for play and marks each one approved for the game. The rule says the footballs “shall remain under the supervision of the Referee until they are delivered to the ball attendant just prior to the start of the game.” The referee for the game was Walt Anderson. A key question in the investigation is whether the balls improperly passed inspection or were either switched or tampered with after Anderson’s inspection. As the home team, the Patriots were responsible for having someone handle the footballs on each sideline.

BALL CONTROL

Footballs are sent directly to teams. Equipment managers can brush them and even use a damp towel to rub off the oil used to preserve the leather to the preferences of each quarterback. The quarterbacks can even practice with the footballs during a game week as long as the footballs remain in good enough condition to pass the referee’s inspection as a new ball. Each team brings at least 12 balls each, so Tom Brady threw footballs provided by the Patriots while Andrew Luck handled footballs brought by the Colts.

POTENTIAL PUNISHMENT

If the NFL finds anyone with the Patriots under-inflated the footballs, Commissioner Roger Goodell has wide latitude for punishment. This includes a fine that can be as low as $25,000 for anyone deemed responsible for tampering with a football, even if it’s the head coach. Goodell could strip the team of draft picks, suspend people for “unfair acts” and reverse a game’s result or reschedule a game.

PREVIOUS OFFENSE

Goodell fined New England Coach Bill Belichick $500,000 and the Patriots $250,000 along with stripping the team of a first-round draft pick in 2007 for having an assistant spy on the New York Jets’ defensive signals by using a sideline camera.

FURTHER REVIEW

Steelers president Art Rooney II said he expects the competition committee to study whether the rule should change but thinks everyone should use the same balls. “It would seem to be simpler to have one set of balls, which was the case for many years,” Rooney said.