The bottom of the backboard (I'm assuming you literally mean the backboard - not the support behind the backboard) is in play. The support behind the backboard (even the part of it that is in the court of play) is out of bounds. There is no offense/defense out of bounds rule involving either apparatus. If a Wake player blocked the ball and it hit the bottom of the backboard and shot out of bounds, it should have been Duke's ball. If a Wake player blocked the ball off the support, it should have been Duke's ball. I assume that either the ball wasn't actually blocked or the officials simply missed the block.