The most expensive skill in baseball is also the most misunderstood -- and the most risky. Why? That was the question Yahoo! Sports baseball columnist Jeff Passan sought explore in his new book, 'The Arm: The Billion Dollar Mystery of the Most Valuable Commodity in Sports.' In this BPIB short, St. Louis Post-Dispatch baseball writer Derrick Goold talks with Passan about the inspiration for the book, the implications of the book, and the ethics of baseball's next frontier -- medical data and competitive advantage within medical advancement. Passan also takes a bird's-eye view of the Cardinals and their place in the new National League Central.