In November, I wrote about the unique running back by committee taking place in Arizona. At the time, Rashard Mendenhall was averaging 3.1 yards per carry, while backup Andre Ellington was averaging 7.2 yards per rush on 54 carries. I thought it would be fun to revisit the Ellington/Mendenhall time share now that the season is over, and to use a slightly different methodology.

Mendenhall ended the season with 687 yards on 217 yards, a 3.2 yards per carry average. Ellington finished his rookie year with 118 carries for 652 yards, producing 5.5 yards per rush. One way to measure the magnitude of the difference in the effectiveness of these two players — and boy was there a large difference — is to simply look at the delta in the players’ yards per carry averages. In this case, that’s 2.36 yards per carry.

Where does that rank historically? Some teams — I’m looking at the Lions in the early Barry Sanders years — gave only a handful of carries to their backup running backs. So one thing we can do is to take the difference in the yards per carry between the team’s top two running backs and multiply that number by the number of carries by the running back with the lower number of carries. In each instance, I’ve defined the running back with the most carries as the team’s RB1, and the running back with the second most carries as the RB2. In Arizona’s case, that would mean multiplying -2.36 (Mendenhall’s average, since he was the RB1, minus Ellington’s average) by 118, the number of carries Ellington recorded. That produces a value of -278.

So what does -278 mean? In the abstract, maybe not much. But I looked at the top two running backs on every team since 1960, and used the same methodology. And only six teams in the last 54 years produced a more extreme value than -278. The most extreme case, by far, came under the watch of the brilliant and affable Todd Haley. In 2010, Thomas Jones rushed 245 times for 896 yards, while Jamaal Charles gained 1,467 yards on just 230 carries. Multiply the -2.72 YPC differential by 230, and you get a value of -626.

Here’s a list of the all timeshares where the second running back outperformed the first and they produced a value of -100 or lower, using the methodology described above:

I’ll let you guys scroll through the table and comment on what you find interesting. Here’s something that jumped out to me (remember, the table is searchable and sortable — you can type in ‘nyj’ to find all Jets pairings or ‘pit’ to find all Steelers pairings, and so on). BenJarvus Green-Ellis appears in the table in each of the last four years with four different backup running backs.

What about the numbers from last year? ^[1]Note that I am only comparing the top two running backs. So in Minnesota, Toby Gerhart produced a fantastic YPC average, but since he ranked 3rd on the team in rush attempts, he is not included. A negative number means the backup averaged more YPC, while a positive means the starter averaged more YPC. Here’s the full list, from Mendenhall/Ellington and Trent Richardson/Donald Brown to the teams where the running back with the most carries produced a higher YPC average than the running back with the second most carries: