A has ball 3rd and 5 from their own 30. A12 completes a pass to A80 at the 37 where A80 runs 5 more yards to the 42 before being tackled. During the run A85 holds B55 at the 38 yd line. Explain what happens in enforcing the holding penalty on this play that is accepted by B.

The hold was during the run after the completed pass. The hold was on the 38 which is behind the basic spot(end of the run). Therefore you will have a 10 yard penalty enforced from the spot of the foul. It will be 3rd and 7 for A from the 28 yard line.

Canadian Ruling
 

Yards were gained, so the hold is applied from Point Ball Held at the time of the hold. If the hold was at the 38, I'm guessing that the ball was near there, because the further the gets is away from (and ahead of) the ball, the less important calling that hold becomes. Let's say that the Point Ball Held was the 38 yard line, when the hold occured. Team A keeps their earned first down, but scrimmages so 10 yards back, A 1D/10 @ A-28.

Good call Keystone. Good to know someone is holding down the fort up there in PA!!