when is possession gained

[wedickinson]

During a scrimmage kick (punt), the ball is snapped over K1's head. K1 along with a couple of R players scramble for the loose ball. As K1 attempts to gain possession of the ball, he is contacted by R1. R1 one then places a hand on top of the ball while his knee is on the ground and pushes himself off the ground. He picks the ball off the ground and runs into the endzone. What's the call?