A Curl route, also called a button hook, is a pattern

Route (football)

A route is a path or pattern that a receiver in American football runs to get open for a forward pass.-List of common routes:*Curl route*Drag route, also called an "In route"*Corner route, also called a "Flag route"...

 run by a receiver

Wide receiver

A wide receiver is an offensive position in American and Canadian football, and is the key player in most of the passing plays. Only players in the backfield or the ends on the line are eligible to catch a forward pass. The two players who begin play at the ends of the offensive line are eligible...

 in American Football

American football

American football is a sport played between two teams of eleven with the objective of scoring points by advancing the ball into the opposing team's end zone. Known in the United States simply as football, it may also be referred to informally as gridiron football. The ball can be advanced by...

, where the receiver appears to be running a Fly pattern but after a set amount of steps or yards will quickly stop and turn around, looking for a pass. This generally works best when the defending corner

Cornerback

A cornerback is a member of the defensive backfield or secondary in American and Canadian football. Cornerbacks cover receivers, to defend against pass offenses and make tackles. Other members of the defensive backfield include the safeties and occasionally linebackers. The cornerback position...

 or safety commits himself to guarding the fly and is unable to stop quickly enough to defend the pass.

The curl is a pattern used frequently by the West Coast offensive scheme

West Coast offense

In American football, "West Coast Offense" refers to two similar but distinct offensive-strategic-systems of play: the "Air Coryell" system; or more commonly the pass play system popularized by Bill Walsh...

, where quick and accurate passes are favored.