you're right, there is a very good reason that he fell to the fifth round but it's not what you're intimiating at- he's still an athlete as a football player rather than a running back or a safety (the two positions he played in college).
he can run fast, he's powerful, but he doesn't have good vision and doesn't always hit the right hole. a very raw, raw player that has only played 2 years of running back.