The running back position was once the most valuable position in football. Teams would only attempt 15-20 passes a game and let their running backs dominate the opposing defenses. As the NFL has evolved into a passing league, the running back position has evolved with. Backs became duel-threats in the running and passing games and today, it still remains one of the most dominant positions in the game. The rankings were determined by the following factors: career rushing yards and touchdowns, yards from scrimmage, pro bowls and first team all pro recognition, yards per carry and yards per game, and years played.
Stats & Info: (pro-football-refrence.com)