In gridiron football, the chain crew (commonly known as the "chain gang") is a crew that manages signal poles on one of the sidelines. There are three primary signal poles: the "rear rod" that marks the beginning of the current set of downs, the "forward rod" that marks the line to gain, and the "box" that marks the line of scrimmage. The two rods are attached at the bottom by a chain exactly ten yards long, while the "box" displays the current down number.
The chain crew, under the direction of the head linesman/down judge, signals the officials' decisions; it does not make decisions. Players look to the chain crew to see the line of scrimmage, the down number, and the line to gain. Officials may rely on the chain crew after a play (incomplete pass or penalty) whose outcome depends on the original spot of the ball. This also includes bringing the chains onto the field whenever an accurate measurement is needed to determine if a first down has been made.