A1 shoots from about 10 feet from basket. B1 comes from A1's side to block shot, he misses and falls to the floor in front of A1. While B1 is on the floor, the rebound comes off the rim above him. A1 grabs the rebound as B1 stands up directly into A1's chest. Is A1 in B1's verticle plane or is B1 causing the contact?