We've already learned about the end zones. All scoring happens here and each team gets one to defend.
The line at the front of the end zone is called the goal line.
Breaking The Plane
On scoring opportunities that require a team to carry or catch the ball in the opposing team's end zone, the ball must break the plane of the goal line for it to count.
Officials are standing on the goal line to make sure that the ball breaks the imaginary 3D plane of the goal line. Yes, you read that right. It's an imaginary 3D plane and it looks like this.
The ball must break this plane for a score to count.
As a referee, there are situations where this is to close to call. That's why we have instant replay so officials can review the play in slow-motion.
Officials will use the two (2) orange pylons that are on the goal line as a reference point to see if the ball breaks the plane.
The ball must pass above and stay within the pylons for a score to count.
A coach may throw a challenge flag onto the field, if he believes a mistake was made by the officials. A coach's challenge requires an immediate review of the last play via instant replay.
In addition to breaking the plane, officials will also make sure that the player stays inbounds on the play. You can learn more about the boundary lines here.