Momentum on a kickoff

[mutzman]

I'm drawing a mind blank here so hopefully someone can help me out....

K kicks deep and catches the ball over his shoulder at his own 2 yard line. Before he can get turned around he A. runs into his own endzone and B. is tackled there.

Is this a touchback or does momentum apply and it comes back out to the 2 yard line? We've argued this in circles and wanted to bring it to this group.

Thanks!!