Touchback?

[Tom Cook]

This play was described to me by my brother, the coach. As a punt rolls towards R's end zone inside the one yard line, K2 "grabs" the ball, and "goes into the end zone". My answer was that K2 has to have posession, ie: control and a foot down inside the goal line or it's a touchback. What is the Fed. rule? Does the K2 player have to stay out of the endzone, or does he just have to have "posession" before going into the endzone?