Picking the NFL's top running backs? A relatively easy proposition. Start with Adrian Peterson, add in clear-cut stars like Ray Rice, Doug Martin, Arian Foster and it doesn't take long to split the best from the rest. Figuring out where each team's overall backfield ranks is a little trickier proposition. How do you weigh a team with an upper-echelon lead back and a depleted depth chart behind him? Or how about the teams with two or three solid backs but no real unstoppable talents? Oh, and what to do with the fullbacks? The rankings here try to take into account everything the 32 NFL backfields have to offer, in order to determine the top combos. Have at it.