Forward Progress

[The Roamin' Umpire]

Originally Posted by AZ_REF

But if forward progress was over the endline it wouldn't be a live ball anymore.

This is a fair point, but the answer lies in 2-28-2 and 8-2-1b. The definition of OOB says nothing about forward progress - the receiver's not OOB until he touches OOB. And the rule on touchdowns doesn't mention the end line - it just says that a player has possession of a live ball on or beyond the opponents' goal line.

If you're still not convinced, consider this play: Receiver reaches over the end line to make a catch, with his feet still inbounds. I expect you'd rule TD on that play, and your example is more-or-less eqivalent.