You need to understand the importance of strengthening your back side. You MUST have the breaking power in your backside, to allow your front side, to perform at its peak. This drill done correctly, can “on average”, increase of your fastball by 1-3 mph, in a matter of weeks.
Also notice his hips are first. This is to “train” our hips and shoulders to separate. The separation is where all our torque, is built up.