Free thrower violation
 

NFHS

A1 has the ball at his disposal to attempt a free throw. As he bounces the ball a few times he also has a foot on the free throw line. Is this a whistle and violation immediately, or does he have time to move his foot back until the time he shoots the ball?

This should be fun.

I'll just say I've never called that specific violation.

I would say it is a good time for some preventive officiating. Step closer and say "Shooter watch your feet-I am." If he/she ignores violation.
;)

This is by rule 43.2.3 a violation. But would I call it?
No.
He doesn't gain any advantage and the opponents doesn't gain a disadvantage, if he puts the foot on the line for a second and then moves it back, I don't care.
And if you would call it, what if he moved back and accidently put a foot on the line at the back of the semi-circle, that's also a violation, but should it be called? imo no