Your non-hitting arm plays a specific role during the follow through. In the video clip above I first extend my other arm way back as I follow through. Next, I keep it more toward the side. What you may notice is that the further I extend my non-hitting arm back, the less my upper body rotates during the follow through.
This is an important concept to understand because you want to be able to control how much your upper body rotates during the follow through. We will get into more specifics about why you may or may not want to control this rotation in other videos, but it’s worth knowing that your non-hitting arm controls how much you turn.