[Ref in PA]

First I disagree that B1 does not have LGP. There is a simple definition of legal guarding position 4-23-2. All you need is two feet on the floor and be facing the opponent. Your LPG may not be very good (as far as defending the basket), but you still got it.

LPG is important for judging contact. The key to judging the contact is in 4-23-3-c. This basically says the defender cannot be moving toward the opponent when the contact occurs. You judge this contact not in relation to where the basket is, but in relation to the movement of the two players involved. If you deem A1 moves into B1, then the foul is on A1 and vice versa.