Chris Beardsley is a biomechanics researcher and author of a book about scientific posterior chain training. He wrote an article up for Mike Reinold's blog this past winter on leg strength and power in baseball pitching.
The article discusses the research that has looked at leg strength in baseball pitching with regards to pitching velocity, injury, and overall mechanics. As Chris points out very early on in the article, there has not been a lot of research done in this area. The two fundamental questions Chris focuses on are:
1. What does the research say about proximal-to-distal kinematic sequencing in pitching?
2. What does the research say about leg muscle activity in pitching?
Check out the article and the evidence behind leg strength in pitching. It might just help you focus your rehabilitation programs on pitchers a little better with return to sport.