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.

Three members of the chain crew hold poles upright. The bottom of each pole is placed along a sideline to denote a line across the gridiron to the opposite sideline.

There may be additional chain crew members. A "clip man" is discussed below. In the NFL, additional chain crew members have additional tasks, such as to relieve the line judge of the clerical task of recording all assessed penalties. Despite the use of "man" in the colloquial terms for the chain crew positions, women can perform any of them.

Members of the chain crew are usually picked by the offices of the home team instead of the league or conference. In the NFL, members of the chain crew must have credentials entitling them to access to the field, and must wear white shirts. The home team pays them; some teams pay an hourly wage and others pay a flat rate to work a game.

The chain crew does not wear protective gear as players do. A routine instruction by officials to the chain crew is to withdraw or drop their signals, and move back, if the play comes toward them so as to endanger them. Often, the signals use bright orange color, are padded, and have break-away components for safety.

For games at all levels except the NFL, the chain crew operates on the side of the field opposite the press box (usually the visiting team's sideline).

In the NFL, the chain crew switches sides at halftime; the referee determines their initial placement.