The last ten years have seen a huge shift in the way that football is played. But whilst every new generation of players improves upon the last, this change has happened away from the pitch, in rooms full of statistical analysts who pour over every pass, shot, and crunching tackle in an effort to fine tune the team's performance. With unprecedented access to the backrooms of the biggest clubs in the world - Liverpool, Manchester City, Barcelona and Juventus - New York Times journalist Rory Smith explains how this revolution has taken place and what it means for the future of the beautiful game.