Is This One?
 

This happened last night, and I was wondering if this is a situation you'd not allow a sub to enter:
Ball is just barely at the disposal of the free throw shooter. The table then hits the horn for a substitute. Since the horn obviously disconcerted the free throw shooter, I killed it with a whistle. We then did not allow the substitute on the premise that it was not signalled in time.
Can't find anything in the book about it other than the allowance of any substitute on a whistle.
We were being dorks, or were we correct?

It was not it time until you killed it with a whistle. Now the sub can come in, but the timer must write chseagle on a piece of paper 1000 times after the game.