I think an important part of this rule is to make runs that end behind the LOS have the basic spot as the previous spot. So essentially, the end of the run (or basic spot) can never be behind the LOS.
This could also clean up definitions and therefore make loose ball plays only happen during a legal pass or kick. Simple. Easy.
But not "fair" to B.
1. A CHOSE to design & run a play, that involved retreating, to counter B.
2. the chosen play FAILED as B was able to contact A behind the line.
3. to prevent, or avoid, loss from that contact, A CHOSE to foul.
4. B achieved 2 goals; thwarting the design/intent of A's decision to gain advantage by retreat, to avoid B, and having A foul B to avoid loss of yardage.
A made two mistakes; (but only 1 foul)
1. Designing a play that failed to counter B's pursuit.
2. Fouling to prevent B's pursuit from causing (further) loss.
What did B to wrong?
If B were guilty of fouling;
1. B still achieved it's goal in breaching A's plan by contacting A where they chose to retreat,
2. However, B chose to foul in order to end the play, at some point BEHIND the previous spot.
Both A and/or B's fouls happened at a "Succeeding spot", which is where either is enforced.
