15yd facemask foul by K on scrimmage kick.

[Fiji07]

Had this in our game Friday and I think we messed up the enforcement of this penalty.

K 4-7 @ K40 lines up in scrimmage(punt) kick formation. Ball snapped and kicked w/o any problems after kick K67 and R35 are engaged @ the 50. K67's hand gets up on R35's facemask and twists. Flag thrown for 15yd facemask. R23 receives kick @ the R 15(after foul by K67) and returns it to the R20.

We enforced this from the end of the run but believe that to be incorrect and we should have enforced it from the previous spot and replayed the down.

Please let me know what you think is correct and give any case book or rule references if you have them.

Thanks for the help.