Football Down Line
Football Yellow Line
Football Chain Crew
The chain crew is a group of referees responsible for marking the first down line on the field. They are called the chain crew because they carry a massive to chain to measure the distance between the ball and first down line.
Football First and Goal
If there are not ten yards on the field between the line of scrimmage and the opposing team's end zone, the goal line becomes the first down line. You'll sometimes here announcers say first and goal. This means the first down line is now the goal line.