Forward Progress after COP

[Suudy]

Watching a game this weekend of an interception in the EZ, I had a thought about forward progress.

1st and 10 from the B 20. A throws into the EZ and B20 intercepts the ball 2 yards deep in the EZ. A5 hits B20 and drives him into the field of play where B20 is tackled on the B2.

1st and 10 from the 2? Or a touchback and 1st and 10 from the 20?

I think this because of the case where B intercepts and tries to go down (to get the touchback). But A drives B onto the field of play to intentionally prevent the touchback. You can't call B's forward progress stopped (since he's obviously going forward). But do you allow A to prevent the touchback?