Train wreck with no LGP

[ABO77]

So why have rule 4-23-2 for "initial LGP" if you have rule 4-23-1 "Every player is entitled to a spot on the playing court provided such player gets there first without illegally contacting an opponent."

Lets say B1 never obtains initial LGP facing the basket and see's A2 in the distance driving for a layup. Several steps before A2 goes airborne B1 slides into A2's path and then A2 lands on B1's back.

Again, I dont understand the purpose of 'initial LGP' if a defender can guard without it.