When Kyle Shanahan became the NFL's youngest offensive coordinator in 2008, he had one prevailing rule: Tell me the why. If a colleague couldn't justify his position by providing the unassailable reasoning behind it, he was told to get the hell out of Shanahan's office. Shanahan and the members of his coaching tree--including Sean McVay, Mike McDaniel, Raheem Morris, and Matt LaFleur--came up in a sport where innovation was the exception, not the...