It’s 3rd-and-5. The quarterback is under center. The crowd is roaring. The quarterback barks hard and someone on the defensive line jumps. Flags fly and the wing officials come running to the referee to report an infraction. The referee intones, “Offside. Defense. Five yards. First down!” When the line to gain is five yards, how do the officials know that it is truly five yards to a first down? What if it is five yards and one inch?
The head linesman and the chain gang have a pretty basic way to know the difference. Before the game, the head linesman inspects the chains. He measures the links in the chains against the yard lines to make sure the markers are a true 10 yards. Say he puts the first pole down at the 20-yard line, and checks the second pole to make sure to reaches the 30-yard line. Satisfied, he then he walks to the 25-yard line and marks the five-yards with a piece of athletic tape. During the game, if the down box is behind the tape marker, the crew knows that a five yard penalty will not result in a first down. If the down box is in front of the tape, he’ll let the referee know, “Five’ll get you one,” so a five-yard penalty on the defense will result in a first down.
This method prevents arguments over whether or not the umpire shorted a team an inch during his penalty walk-off and prevents the referee from having to bring the chains in to measure for a first down after a simple offside penalty.
The NFL does not have a prescribed mechanic to see if five-yard penalties result in a first down. It is up to the head linesman to control the chains, know the line to gain, and know if five-yard penalties will give the offense a first down. With all the technology — calls for laser markings and computer chips in the football — sometimes chain links and a piece of tape are all officials need.