Follow-Through Interference?

 
With a 1-1 count on the batter (B1), the runner on second base (R2) is stealing on the pitch. B1 swings hard at the pitch, misses it, but B1's follow-thru hits the catcher in the helmet, causing the catcher to drop the pitch. R2 arrives safely at third base.
 
The defensive coach wants some kind of penalty for the batter's follow-thru hitting his catcher. The offensive coach argues that R2 was easily safe at third base, so ignore the follow-thru contact.
 
What does the umpire do now?
 
Call
In NF, follow-through interference is when the bat hits the catcher after the batter has swung at the pitch and the catcher is hindered on his attempt to make a play on a runner (NF 2-21-4). In NF (and only NF), the penalties are similar to other more common batter's interference (described in NF 7-3-5).
 
For NF, in the situation below, the batter interfered, so B1 is out and R2 is returned to 2nd base.