on 4th down and 10, team A punts the ball. at the snap we have illegal motion, while the ball is in the air B35 makes an illegal block in the back. the ball is caught at his own 20 yard line and returned to the 40. the previous line of scrimmage was A's 35. are these offsetting penalties and replay the down? if there was no illegal motion we would have a psk foul.

R may decline the penalty against K and keep the ball. Obviously K will accept the penalty (PSK) foul for the illegal block in the back and R will have the ball 1st an 10.

See the case book 10.2.1 Situation D.

Yes it would be a PSK foul if no foul on Kickers (actually a PSK in both situations)

The B foul was while the ball was in the air --- they did not gain possession with "clean hands", thus they cannot decline the A foul. These fouls offset.

This is a psk foul in NFHS. R may keep the ball by declining the foul on K and having their penalty enforced from the end of the kick (hopefully the BJ has a bean bag down to mark the end of the kick). Or R may create a double foul by accepting the foul on K and replaying the down from the previous spot. In this situation K has no penalty options. R is the team in final possession and the decision to accept or decline the penalty rests with R.

I agree PSK applies in either case - assuming K's block was beyond the ENZ. That is the unknown eliment he left out.

I agree PSK applies in either case - assuming K's block was beyond the ENZ or beyond NZ after kick crossed ENZ.