[Adam]

Originally Posted by JS 20

I went and re-read the rule and then asked myself why it was in place. The best thing I can come up with is that it puts the defense at a disadvantage to steal, tip, etc. the pass when you're behind the board and pass it over the top to someone on the other side. That said, the defense has the exact same opportunity to block the shot in the corner that they have anywhere else on the floor so it shouldn't matter in that instance. Just my $0.02

Camron has told us the origin of the rule:

Originally Posted by Camron Rust

Its a matter of likelihood in combination with the original reason for the rule. The rule came about when Wilt Chamberlain's team would lob a baseline throw-in over the board for him to slam in. If I'm not mistaken, the NBA and most, if not all of D1, had converted to rectangular backboards by his time. It was a completely indefensible play...so they made it illegal for the ball to cross over the top of the board. There is rarely a "normal" play where the ball also goes over a rectangular board. As for fan shaped boards...they're much smaller and it is much more likely for a ball to go over the top in the course of normal play. Not wanting to stop the game unnecessarily and knowing that fan boards were used in places not likley to be affected by Chamberlain-like players, there was no need to illegalize it for fan shaped boards.