[bossref]

Yeah, the top is ok.
But the ball cannot pass over the board
from either direction.
The rule was written because in 1957
at Kansas U there was a rather tall
player named Wilt Chamberlain.
They ran an out of bounds play with him in the key.
They simply tossed the ball over the board for
an alley-oop slam dunk. It wasn't very fair since
the Stilt was so much bigger than everyone else.
Larry Bird's version of shooting the
ball over really didn't gain him any advantage.