Batters box question

[danreeves1973]

Calling Dixie League 9-12 boys, using modified OBR

Have a batter that refuses to stay in the box once the pitch is thrown, be it inside where backing up is warranted or head high outside or right over the plate. Kid actually jumps back on one pitch that is over the plate and falls down. Ends up walking. Defensive coach asks me after the inning why I didn't call a strike every time the kid backed out of the box. Just to humor him, I looked it up today and I can find nothing that says once the pitch has been thrown that the batter cannot leave the box without penalty if he doesn't swing at the ball. I do realize that what the kid is doing is bad baseball and his coach needs to work on this problem.

So my question, is there any penalty for the batter stepping out of the box ONCE the pitch has been thrown, not during the set or windup per 6.02 (b) OBR? Again, he did not attempt to strike at the pitch.