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. Members 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. A "rod man" holds the "rear rod" that marks the beginning of the current set of downs. Another "rod man" holds the "forward rod" ten yards toward the defense's goal-line from the rear rod. This marker indicates the line to gain, which the offense must reach in their series of four downs in order to retain possession of the ball. The two rods (sometimes known as "sticks") are attached at the bottom by a chain exactly ten yards long. The chain is always taut so that the rods are ten yards apart. The "box man" holds a pole that marks the line of scrimmage. 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