When you lead with the head, it feels like you use it to lever your shoulders through for more pace.
Try throwing a ball facing sideways, or even at your release point. It locks your shoulders there.
Try throwing a ball facing your target (meaning your head, not your torso or legs), and your rotation is much cleaner and easier to do
You KNOW where the ball is, you tossed it up?
You need to look at the incoming groundie, because your adversary hit it to you.,