When looking at Shane Bieber it is obvious that he has a short arm action. Looking at him through a different lens you see that the timing of the front foot landing and the arm getting in the correct position is the same as guys with longer arm actions. His shorter arm path and arm action allows him to break his hands later and hide the ball better with his body (something that Zach Greinke does extremely well). Shane also counter-rotates his upper-body after breaking his hands which is deceiving and can allow for better hip to shoulder separation if it is executed with proper posture and timing. He tilts his posture back early, after the peak of his leg lift, in order to get his lower body started down the mound. This move locks in his posture for the rest of his delivery until his front foot hits the ground. By the time his front foot hits the ground his head is over his belt and he is stacked over his body (side view). This allows him, and every big time MLB pitcher to get great extension and throw the ball downhill, closer to the plate. Downhill and closer to the plate = higher “perceived” velocity.