In the NFL and presumably in most football leagues, the goal lines, yard lines, and hash marks are all four inches wide. The hash marks/yard lines are painted at 36-inch intervals; that is, they are 32 inches apart so that they mark exactly one yard each. Easy enough.
However, doesn't this make the field between goal lines exactly 99 yards and 32 inches from goal line to goal line? It is less than one hundred yards, right?
Since that cannot be, I must conclude that the rear of the defensive goal line is the actual defensive goal line. Am I right?
Come to think of it, this would be consistent with how balls are spotted. On a touchback, for example, the ball is spotted with the nose just kissing the back edge of the 20-yard line. Thus a ball spotted at the one-yard line would just kiss the painted hash mark, and so a ball spotted at the one-inch line would be three inches behind the front of the goal line, which we normally think of as "in the end zone," but it must not be so.
I suppose it would only matter in the question of a loss of yards from scrimmage or a terrible kick return within four inches of the goal line. If a ball carrier is down by contact with the nose of the ball spotted three inches behind the front plane of the defensive team's goal line, this must not be a safety/touchback, right? That is, the ball can be spotted for a play from scrimmage with its nose at three inches behind the front of the painted goal line (one inch from the back of the painted goal line), from which the offense would have to advance 99 yards and 35 inches for a touchdown. Is this right?