No discussion of RBis complete without discussion of the OL in front of them. So we'll begin there. Football Outsiders does a great job of comparing offensive lines in the running game. You can read their full analysis by following the link, but I like to take their analysis one step further. They calculate Adjusted Line Yards: Based on regression analysis, the Adjusted Line Yards (ALY) formula takes all running back carries and assigns responsibility to the offensive line based on the following percentages:
Losses: 120% value
0-4 Yards: 100% value
5-10 Yards: 50% value
11+ Yards: 0% value
In other words, the OL is to blame for negative runs, gets full credit for runs of 0-4 yards and diminishing credit for longer runs with no credit for runs over 10 yards.