[Mike L]

I understand what cut-off means. I also understand that blanket statements like "You cannot cut off a receiver running a route" are dangerously misguided. To go back to the 2007 casebook example it states
B3 gets in the path of a receiver (sorta sounds like a possible "cut-off" huh?) A4 without making contact. B3's presence results in (a) A4 slowing to avoid contact or (b) A4 inititaing contact in an effort to reach the ball. No foul in (a) but a foul in (b) by A4 for OPI (which sounds even more like the OP).
So it continues to go back to who initiates contact by the cut-off. You can dance around it all you want by claiming cut-off means a certain thing that you implied, but it still remains as I said you have to determine who caused the contact to initiate. Just because B steps into the path of A's route does not mean B initiated the contact.
And as a side, if you want to talk about things not remotely related to the subject, just how does B step into the route of an A receiver who has turned away from him? Or how can you say A is no longer a potential blocker. If B manages to get in A's way without initiating contact, isn't A now coming at him?