[rwest]

Assuming the OP but make one minor correction. Lets say B1 is attempting to get up when A1 trips over them. Are you going to call a foul? If you do then might I suggest if you believe B1 is entitled to lay prone on the ground then you also have to give him that spot on the floor all the way to the ceiling due to the principle of verticality. A player is allowed to move vertically from his spot on the floor.

Now I would have a foul, becuase I don't believe that player is entitled to that spot. Now if he doesn't move, then I have a travel, because the offensive player initiated the contact. A1 didn't have to attempt to go over B1 laying on the ground. He chose to and he is the one that caused the contact.

Remember, when interpreting any document you must take the entire document into consideration. If the player is entitled to lay prone on the floor then they are entitled to verticality from that same spot to the ceiling.