[Ref in PA]

What I see a lot is A1 is going for the loose ball and diving for it. B1 has a clear path to the loose ball but instead dives to put his body between the ball and A1, contacting A1, essentially pushing him aside. It is a little like boxing out, but B1 does not have the previously established position. To me that is a foul on B1, it is a blocking foul. If they were standing up, you would not let that kind of contact go on, yet when there is a loose ball, many refs allow all sorts of contact go.