[Nevadaref]

Originally Posted by Indianaref

Interesting that this topic has just been brought up. Indiana's 3A girl's state final had a situation towards the end of game that had an inadvertent horn during a free throw. The lead official whistle the ball dead while the throw is in the air. He waived off the shot, which I thought at the time was something he didn't have the rules backing for. Here is the link, scroll to 1:41:53 to see the situation.

2014 IHSAA Girls Basketball 3A State Championship | Indiana High School Athletic Association Videos | iHigh.com

If the ball is already in flight, he doesn't have rules support to cancel the try! In that particular circumstance, even a whistle would not cancel the try because it is already in flight.
He can stop it before the release.

Here is the NFHS Case Book play providing this principle:

6.7.5 SITUATION:
A1 is at the free-throw line for the second of two attempts. After the ball is at A1's disposal, B1 commits a lane violation. The administering official inadvertently sounds his/her whistle: (a) before A1 starts the free-throw motion; (b) after the ball has been released; or (c) during A1's motion but before release of the ball.

RULING: Whether or not the whistle was sounded inadvertently it has the same result. In (a) and (c), the ball becomes dead immediately. In (b), the whistle does not cause the ball to become dead until the free throw ends. Because B1 violated, in all cases, a substitute throw is awarded if the free-throw attempt by A1 is unsuccessful. (4-20-3)