Now you have changed the situation a bit.
In this case, with the batter stepping out of the box, and that action causing the pitcher to not release the ball, the umpire should declare a "No Pitch", and all action is cancelled.
Depends on the umpire if it will get called like this or not. My first year as a head coach, my DD pitching, in 10u, something close to this happened. DD thought that she saw the batter moving out of the box and the umpire not looking while she was in her windup. She held the ball. There was a runner on 3rd. Umpire called illegal pitch and the runner on 3 was allowed to score. I go out and ask her what happened and she said she saw the umpire not looking and the batter moving out of the box, looked the same to me sitting in dugout. Talked to umpire and of course he said he was looking at her the whole time and the batter didn't move. This was last inning and we were up by 1, illegal pitch now tied the game. 2 outs, 2 strikes on batter. Batter struck out next pitch.
Game went to ITB and we ended up losing.