The yard line in football is a line on the field that denotes a single yard in length. There are 98 yard lines on a football field each with its own name like the 50 yard line. Yard lines count up from the 1-yard line and are duplicated, meaning there are two of each yard line, but only one 50 yard line. Yard lines come with field numbers every ten yards to helps players and fans see the location of the ball. The field is 100 yards from one goal line to the other, and they extend out to each of the sidelines. Regardless of the player's positioning, he knows where he is positioned because of yard lines.
On the Field
Sideline officials, like the field judge and side judge, carry a yard line marker so that the players can see exactly where their down and the ten yard goal is located. The yard lines are extremely important for all officials, too, so they can ensure that the game is being played fairly.