Not all hitters swing on the plane as the pitch. A slight upswing at the same angle which the pitch is oppositely going down gives you a better chance at contact, which Ted Williams advocated so strongly in his book 'The Science of Hitting' (recommended btw). On outside pitches, Beckham has shown ability to take a slightly downward swing until point of contact then quickly roll his right wrist over, creating tremendous backspin on the ball. This video is a great example, clear to see around the 36 second mark.
http://chicago.whitesox.mlb.com/media/vide...tent_id=6466723
The backspin is what causes the ball to carry and fool Ellsbury. Stone comments about the ball "slicing away" and "just taking off". The opposite effect occurs when you swing at an angle steeper than that which the ball is coming down at and put topspin on the ball, or a humpback line drive as Hawk would call it