PARIS (AP):

Scuffed balls, scratched balls, balls switched mid-game. Suspected ball-doctoring isn't only an issue for the NFL, which is investigating a report that the New England Patriots used underinflated footballs in the AFC championship game, while beating the Indianapolis Colts 45-7.

A look at dirty tricks in other ball sports:

CRICKET: Ball-tampering is so common in cricket that some of the sport's most famous names have argued it should be legalised.

Spitting sugary saliva on the ball, gouging at its leather covering with fingernails or biting it, picking at its seams, scuffing it with dirt, bottle tops or sandpaper are some of the ploys used by teams over the years, to alter the bounce of the ball and flight through the air to make it harder for batsmen to hit.

TENNIS: During a changeover at the 2013 Madrid Open, Anabel Medina Garrigues was filmed furiously scuffing new balls by rubbing them hard, one after the other, against her racket strings - apparently to make them slower and take some sting out of the game of opponent Serena Williams. Williams still won 6-3, 0-6, 7-5.

In a statement, the WTA said: "Had the umpire witnessed the scuffing of the balls, the umpire would have instructed the player to stop."

SOCCER: In Premier League soccer, supplier Nike provides each team with 120 match balls for each season. One ball is used per game and match officials check, before kick-off, that it is correctly inflated. Players can ask the referee to look at the ball and have it replaced if they believe it is incorrectly inflated.