Editing Chain crew (section)

==Operations==
At the start of a series of downs, the linesman stands so that the heel of one foot marks the initial [[line of scrimmage]]. The box man places his indicator to mark this position and sets the box to display "1". The operator of the rear rod marks the same position, while the other rod man moves ten yards toward the defense's goal line to mark the line to gain.

The linesman, the box man, or a fourth member of the chain crew attaches a "clip" to the chain to line up with the rear edge of the closest five-yard line to the rear rod.<ref name=Schultz>{{Cite web
|url=http://www.footballzebras.com/2012/11/27/the-head-linesman-and-chain-gang-use-special-equipment-to-keep-chains-accurate-on-the-field/
|title=HL, chain gang use special equipment to keep chains accurate on the field
|author=Mark Schultz
|publisher=FootballZebras.com
|date=November 27, 2012
|access-date=January 6, 2017
}}</ref> A device on the clip indicates which numbered line this is. The clip and the device let the chain crew restore the position of the rods after a mishap. In leagues such as the NFL with [[Instant replay in American and Canadian football|Instant Replay]], there may be multiple clips to let the rods be repositioned after a play is reviewed and reversed.<ref name=Schultz />

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. After a play that results in a first down, all three members move and reset their signals to mark a new series of downs.

The chain crew must not move until the referee or linesman signals whether the play finished without a penalty. On a penalty, the chain crew stays put so that the officials can see the original state. When the referee and linesman walk off the appropriate number of yards, the box man moves as well. The box man does not change the number displayed, except on a penalty that results in a loss of down. On a penalty that results in a first down, the entire chain crew moves and resets.

When possession of the ball switches to the other team, the forward rod becomes the rear rod and ''vice versa'' to minimize the distance the rod men have to move. However, at the end of the first and third quarters, when players switch directions on the field, the chain crew also moves (for example, a marker may move from one 32-yard line to the other 32-yard line). The rear rod man moves past the forward rod man and continues to mark the start of the series of downs, in the new orientation. The linesman and other officials supervise this movement, using one or more clips to exactly reposition the chains.<ref>{{Cite web
|url=http://coloradofoa.com/chain-crew-end-of-quarter/
|title=Chain Crew – End of Quarter
|author=Kirk Russell
|publisher=Colorado Football Officials Association
|date=September 9, 2016
|access-date=January 7, 2017}}</ref>

On plays where there is no line to gain (a series of downs that starts within 10 yards of the goal line, a try after touchdown, or a kickoff), the rod men lower or lay down their signals, but the box man continues to mark the line of scrimmage.

===On-field measurements===
[[File:1st down measurement at UCLA at Cal 10-25-08.JPG|thumb|left|A first down measurement during a game between the [[USC Trojans football|USC Trojans]] and the [[California Golden Bears football|California Golden Bears]].]] The chains are brought onto the field whenever the referee needs an accurate measurement to determine if a first down has been made. A team may also request an accurate measurement to determine how far they have to reach for the first down.

===5-yard mark===
Before the game, many linesmen attach a piece of tape at the midpoint of the chain.<ref>{{Cite web
|url=http://skipharrison.com/Sports/ChainGang3.html
|title=Chain Gang
|author=Skip Harrison
|access-date=December 2, 2016}}</ref> The linesman can compare the line of scrimmage to this mark at the start of a play and know whether a 5-yard penalty against the defense will result in a first down. If so, the linesman's typical hand signal to the line judge across the field is to extend the arms with the thumbs pointing toward one another. Such a gesture with thumbs pointing away signals that there are more than 5 yards to gain.<ref>{{Cite web
|url=https://mafiadoc.com/2015-aia-football-officiating-mechanics-manual_59c2b4eb1723dd3c81fd7687.html
|title=2015 AIA Football Officiating Mechanics Manual
|publisher=AIA
|date=July 24, 2015}}</ref>{{Rp|6.10.1}}
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