Football Down Line
Getting a first down allows the offense to get a new set of four downs.
Football Yellow Line
You can see the first down line as a yellow line on TV. You'll notice that the yellow line doesn't move often. The offense must reach or go past the first down line for it to be moved.
REMEMBER: The first down line or yellow line on TV always shows the distance the offense needs to go to get a first down.
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.