Balk-turning the shoulder

[Gre144]

I am using the half wind up in reference to the set position. The term set position is a little confusing because it can refer to the initial position of the pitcher as he steps on the mound or the time after the pitcher brings his hands together to come set.

I am curious if F1, in the the set position, can move his shoulders towards first at the time his hands are down at his side? I know that at the time his hands are together while he is set that he can not turn his shoulders. I am not sure if the shoulder turn is permitted when he is initially on the mound and his hands are at his side.

Greg