Chain crew
In gridiron football, the chain crew (commonly known as the "chain gang") are three people, each of whom holds vertically a signal on a pole on one of the sidelines.
The chain crew, under the direction of the linesman, signals the officials' decisions; it does not make decisions. Players look to the chain crew to see 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.
Members
The chain crew comprises the following members:
A "rod man" who holds a pole (the "rear rod") that marks the beginning of the current set of downs.
A "box man" who holds a pole with an indicator of the current down at the top (the "box").
Another "rod man" who holds a rod (the "forward rod") ten yards toward the defense's goal-line from the rear rod man. This marker indicates a line on the field — the "line to gain" — that 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; when taut, the rods are ten yards apart.