Chain crew

The two rods are attached at the bottom by a chain exactly ten yards long, while the "box" displays the current down number.

Officials may rely on the chain crew after a play (incomplete pass or penalty) whose outcome depends on the original spot of the ball.

In the NFL, members of the chain crew must have credentials entitling them to access to the field, and must wear white shirts.

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.

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).

For professional and college football games, an auxiliary chain crew operates on the opposite side of the field, supervised by the line judge.

In leagues such as the NFL with Instant Replay, there may be multiple clips to let the rods be repositioned after a play is reviewed and reversed.

[2] After a typical play, the box man increments the displayed number and realigns that pole to the new line of scrimmage, again as directed by the linesman.

In the pre-television era, it was a rod (shorter than the height of the operator) with a triangular pointer that rotated to show the official the down number.

It was replaced with a much larger, two-sided flipper system when television became widespread; flipper-style down markers are still in use in scholastic and amateur football.

[7] For the 1974 season, the World Football League used the "Dicker-rod," a proprietary stick approximately 3 yards (9.0 ft; 2.7 m) in length, which allowed measurements to be made with one person instead of three.

[8][9] When the USFL and XFL merged to form the United Football League, they continued to use a similar technology, "TrU Line.

"[10] In July 2024, the NFL announced a partnership with Sony to use the company's Hawk-Eye computer vision technology to replace the chain crew.

The system was tested during selected 2024 preseason games, but the NFL does not plan to fully implement the technology until 2025 at the earliest.