Since Develin took over as the lead fullback in 2013 through this stage of the 2015 season, the Patriots actually average 0.82 fewer yards per carry in the rushing game when Develin is on the field, versus when he is off the field. On the flip side, the Patriots passing attack averages 1.11 yards per play
more with Develin in the backfield. The average passing play jumps from 6.39 yards per passing play (
similar to Chad Henne) to 7.50 (closer to Drew Brees).
Why? Defenses actually have to respect the rushing game when Develin is on the field, and then he's also a threat in the passing game out of the play action. He keeps the linebackers occupied and thinking, while there's zero chance that teams have to account for Mason in the passing game.