My friend Alan Nathan, a retired professor of physics at the University of Illinois Urbana-Champaign and one of the leading experts on the physics of baseball, appeared on the Society for American Baseball Research's SABRcast several weeks ago. The archived audio is available here (you have to scroll down a bit when the new page comes up). Professor Nathan discusses both historical and current trends in the study of bats (and bat swings), baseballs (and their spin, flight, etc.), and baserunners.