Rule clarification - FT violation

[RTPud]

Hey,
I saw something called and I cannot find a governing statement in the rules.
I was hoping someone could provide interpretation, or whether the call was unfounded.

Situation:
First FT out of 2; Shoot has ball.
Opponent lined up between 2 hashes closest to the shoot.
Opponent takes 2 steps BACKWARD (away from the neutral zone).
Is this a violation?
My understanding was "release" was define by entering the neutral zone, but the players' area to occupy extended back a few feet beyond the end of the parallel hash marks.

Anyone point to a rule for this?