I feel like an idiot for even asking, but...
 

A's ball 1st and 10 from their own 25. A7 drops back to pass and completes a pass to A88 who is downed at the A37. Before the pass, A71 held B92 at A's 22-yard line.

How is this enforced? Case Book 10.4.2B seems to say one thing, and 10-6 seems to say another. This particular play has confused me for four straight years now...and reading the book is NOT helping.

A's ball 1st and 20 from their 15. Start clock on RFP.

NFHS- Spot foul 1/23 A's 12, RFP.

JS63 - It's an "All-But-One" foul, because the spot of the foul is behind the basic spot, which is the previous spot for a foul during a loose ball play (including the run or runs preceeding a loose ball, which is when this foul occurred).

NFHS 10-6

1st and 23 from A12. Start clock on RFP.

You have a foul by A during a loose ball play. (10-3-1 Note "The run which precedes such a ...legal pass... is considered part of the action during a loose-ball play.") so the basic spot is the preceding spot, A's 25. The foul is behind the basic spot so the enforcement spot is the 22. Holding is 10 yards so we go back to the 12. It's then A's ball, 1st & 23 from the 12. Start clock on the RFP.

10-40-2b discusses a foul by B, not A

JIm D, 10.4.2B does discuss a foul by A. But I think I see what I was missing - they merely are stating where the basic spot is - they don't say that that's where the enforcement spot is. Since the foul in my scenario occurred behind the basic spot, the foul becomes a spot foul.

Thank you all - sometimes the most simple things are missed...

Gotcha. I looked up the wrong case play.

NCAA: first and twenty from the A15.