Understanding the mechanics of a pitching motion:
Imagine you are pitching, you have just landed your post leg (the leg opposite your throwing hand), and your hips are beginning to open. This is where I require my pitcher to be. First of all, your post leg needs to be planted in a position so that your lower leg is perpendicular to the ground. We call this landing next to a fence, (imagine the fence to be about waist high). We want that shin to be up against the fence, not at an angle away or ahead of the imaginary fence line. The reason we want this is because we want our upper torso, shoulders on up, to be able to reach out and over that fence and throw with maximum velocity. This will also ensure body control which undoubtedly equals pitch control. Some things to look for:
Predominantly, when a pitcher lands on his heel with the post leg, he tends to be too long in his stride, and his shin area will not come up to the fence line Hence, his upper torso will not be able to get over the fence. As a pitcher finishes, his back leg follows his throwing arm to come up with the plant leg. The back leg should not come in front of the fence either. If it does, chances are that the stride is too short, the athlete is throwing across their body, or is opening up too soon. We want the upper torso to go OVER the top of the fence, not through it from the side. Lastly, you should look at where this back foot is planted as the hips start opening up, after the post leg is planted. It literally should be nailed to the rubber. The hips will bring the arm, and as the arm is coming through the slot, then the back leg should lift and plant on the same level as the post foot, so the pitcher is in a fielding position. Remember that for every action (the throwing hand), there is an equal and opposite reaction (the back leg).