Player with the ball turns his back and sets a screen

[Adam]

You judge A1's screen as you would a screen by A2. A stationary pivot foot doesn't mean the player isn't moving; only that he's not traveling. There's a difference. Just like a defender can move one foot towards the offensive player and commit a foul, a ball handler can just as easily move one foot and still be moving into the defender. What you have sounds like a clear player control foul to me.