The yellow line in football is the digital image of the spot of the first down marker used on television to make watching a game easier. The line is a near exact measurement of the 10 yards needed to gain.
Players are not able to see the line on the field when they play. The line is generated by computers and projected onto the television broadcast as a special effect. It may look like it is part of the field because when players run through the line it appears as if they are standing on top of it. That effect occurs because the technology only displays the yellow color on top of the colors green (grass) and brown (dirt).
The yellow line officially made its debut during an edition of Sunday Night Football, September 27th 1998. It was not ready during the first week of the season due to ironing out one final bug, so it was not until week four when it was first aired. Stan Honey is credited with the invention of the yellow line, working with a company called Sportvision. The technology was called First and Ten and generated an overwhelmingly positive reaction from football fans.
Sportvision is still the company in charge of the magic yellow line seen in football today. It beat out rival company Princeton Video Image to remain the premier yellow first down line company. Since its creation the equipment necessary for the yellow line has drastically decreased, now at games only one person is necessary to operate the technology. Although the design still remains the same, the accuracy of it has improved significantly.