No foul on thrower-in at end of game?

[Dennis Bronco]

I am trying to remember if I read about this situation on this forum.
With less than 5 seconds in the fourth quarter and the clock running, A1, whose team is ahead by one point, has the ball for a throw-in. B1 reaches across the plane and either knocks the ball out of A1's hands or fouls A1. I thought the officials were supposed to ignore the fouling attempt (unless it is obviously flagrant) and just let the clock run out. Is that's correct, what is the rule or case? I think the case may be from many years in the past. Thanks much.