Why is an NFL goal line pylon out of bounds?

Answer 1

The goal line is marked inbounds, but extends beyond the in bounds line. The pylon is the point at which the goal line is out of bounds. It is used by the sideline officials (usually deep wings: FG & SG) to determine when a touchdown is scored or not on plays that are at made at one of the four corners of the endzone.

In the NFL, the ball has to be inside the pylon when running into the endzone to be considered a touchdown.

In the NCAA starting this year (2012), and part of the player can touch the pylon and as long as the ball is inside the goal line extended (extending into the out of bounds area), to be considered a touchdown.

In high school, the ball has to cross the goal line extended to be considered a touchdown.