Chain crew - Wikipedia
1st & Ten (graphics system) - Wikipedia
This might be why Louisville's WR went out of bounds a yard early on a game-deciding play - SBNation.com
Amazon.com : CHAMPRO Football Deluxe Down Indicator Box and Chains Set, ORANGE : Football Yard Markers : Sports & Outdoors
First-down line for all to see
Looking Down Sideline of Football Field from Endzone Stock Photo - Image of perspective, marker: 161271286
NFL chain gangs: Everything you need to know about the crews who man the down markers - Sports Illustrated
What the hell do all those lines mean? - The Rookie Playbook
Why the NFL Still Uses Chains to Measure First Downs
How do they make the first down line appear on the football field during a game? - Scienceline
Football Down Marker and Chains
361 American Football Down Marker Photos and Premium High Res Pictures - Getty Images
Down (gridiron football) - Wikipedia
NFL field markings - Fonts In Use
205 First Down Marker Images, Stock Photos & Vectors | Shutterstock
Football First Down Line
First-down spots limit the necessity for too many measurements – Football Zebras
361 American Football Down Marker Photos and Premium High Res Pictures - Getty Images
361 American Football Down Marker Photos and Premium High Res Pictures - Getty Images
450+ First Down American Football Stock Photos, Pictures & Royalty-Free Images - iStock
Creator of NFL's yellow 1st-down line inducted to Inventors HOF
The History of Using the Chains to Measure a First Down | NFL Films Presents - YouTube
Why the NFL Still Uses Chains to Measure First Downs
