It is a plane, which means it is infinitely wide. Technically, it even extends infinitely down underneath the field. A plane extends infinitely in all directions within two dimensions.
Any time the ball crosses that plane while the player is inbounds, it is a touchdown. Your case above is clearly a TD.
So let's say a WR stretches out to catch the ball and barely gets his toes inbounds at the 1 yard line, then as he's falling down (with toes still touching inbounds) he stretches out the ball to cross the goal line plane out of bounds, but before any part of his body touches out of bounds. That is a TD.
However, let's say another player runs towards the pylon with the ball and dives from the one yard line. So he crosses the sideline in midair at the one and crosses the goal line plane with the ball out of bounds before hitting the ground. That ball will be spotted where it last crossed the sideline (at the one yard line). Not a TD.
I hope that's clear. It's kind of hard to explain without drawing a picture.
depends of the team ......If its OSU or MU, TD !!!!