Training the lower half of the body usually focuses on the big movements like squats and deadlifts. They dominate the landscape for most athletes, and rightly so. When you look at a pitching motion, the majority of the actual motion from leg pickup to release is performed through an interplay of single leg motion. That interplay could fill a novel, but the main concept is that each leg individually plays an important role in pitching.
This article details my thoughts on our developmental baseball athletes and lower body training. It was written for and can be found at http://www.simplifaster.com.