This drill is meant for the pitcher that likes to swing their post leg out away from their body and find themeslves eventually open up or closing too soon.
How It's Done
Get a folding chair and place the back of it close to the rubber towards the third-base side. If the pitcher is left-handed, place the chair close to the rubber on the third base side of the mound.
Let your pitcher assume a wind-up position and begin their delivery. As the pitcher's left leg rises, watch it as it comes down and through the pitching motion. If the leg hits the chair at any time, one of two things is happening:
- That they are swinging it open, causing the hips to open up too soon.
- They are driving towards the third base side of the plate (first base for lefties) causing them to throw across their body.
Finally, as the plant leg is placed, the arm comes through the slot and the back side is released. To ensure a good back side, the right leg must be lifted high enough so that it clears the top of the chair. This ensures that the pitcher is equaling out the force from their throwing arm.
What's Happening
It's all about physics, specifically, Newton's Third Law: for every action (the arm), there is an equal and opposite reaction (the backside leg).
As with any drill, do this in repetition, even while the athletes are doing pen work. It will pay off dividends later, and should keep the pitcher from some serious injuries.