This is our old blog. It hasn't been active since 2011. Please see the link above for our current blog or click the logo above to see all of the great data and content on this site.

Running back deterioration II

Posted by Doug on June 19, 2006

For reference, here is Running back deterioration I.

Tip of the cap to my good buddy monkeytime for suggesting the following study.

Before diving in, though, I want to say something about the point of this study and the previous one. Many of you pointed out in the comments that determining a running back's real mileage is a whole lot more complex than just looking at his career-to-date NFL carries. That is certainly true.

After giving it some thought, I rationalized realized that quantifying workload is not what I want to do here. It's just way too big a job. Rather, my goal for these studies is to see if one simple factor (career-to-date rushes) gives us any clues. If so, great. If not, then maybe that means workload doesn't matter, or maybe it means that we're measuring it improperly, or maybe that means that it's simply too subtle to have been picked up in these studies. Regardless, it means we've got more work to do. But it's hard work and it's for another time. Remember, I started the last entry by asking: Should a 27-year-old running back with 1700 previous career rushes, for instance, be considered β€œolder” than a 28-year-old running back with only 1000? I'm going to continue to focus on just that simple idea.

The idea for this second study is to find all backs who met a certain performance benchmark during their career. For example, we might look for all runners who finished in the Top 12 (by fantasy points) at least four times. Now that's a pretty exclusive group. Lamar Smith isn't in it.

After throwing out the still-active players, we are left with 28 runners. Now we'll count up each of their career-to-date rushes through (and including) their age 27 season. We'll order them from least to most and then divide them into three groups: low mileage, medium mileage, and high mileage. Here they are:

Player Rsh Thru Age 27
James Brooks 426
Wendell Tyler 583
Terry Allen 641
Earnest Byner 672
Herschel Walker 721 LOW MILEAGE
Chuck Muncie 748
Roger Craig 749
William Andrews 793
Lydell Mitchell 801

Wilbert Montgomery 835
John Riggins 928
Chuck Foreman 939
Neal Anderson 947
Lawrence McCutcheon 950
Ricky Watters 990 MEDIUM MILEAGE
Tony Dorsett 1026
Franco Harris 1135
Curt Warner 1189
Marcus Allen 1289

Terrell Davis 1343
Eddie George 1360
Thurman Thomas 1376
Ottis Anderson 1401
Earl Campbell 1404 HIGH MILEAGE
Eric Dickerson 1465
Barry Sanders 1763
Walter Payton 1865
Emmitt Smith 2007

Now we look at their careers from age 28 on:

Mileage N RshAfter27
Low 9 1070.9
Medium 10 1204.7
High 9 1385.2

The backs who had more mileage before age 28 also logged more miles from age 28 on. So again we see no evidence that high mileage backs are having their careers shortened by the early workload.

Obviously, the benchmark had two arbitrary paramters in it: top 12, and four times. If we change it to something else, we'll get similar results. Here are a couple of examples:

Benchmark: top 20 at least five times

Mileage N RshAfter27
Low 9 1070.1
Medium 11 1192.2
High 9 1381.3

Benchmark: top 5 at least once

Mileage N RshAfter27
Low 19 544.4
Medium 20 708.5
High 19 1169.7

I have tried several sets of cutoffs but have not found one where the high mileage group does not come out on top. But I'm still left with the same feeling I had in the first study. Namely, the premise of this study is that we are identifying groups of comparably skilled players. But if you look at those lists you still don't get that feel. Wendell Tyler wasn't a one-year wonder, but he wasn't Eric Dickerson either. Despite meeting the same benchmark, the groups are not truly comparable.

So let's try to stack the deck in favor of the low-mileage group. Let's look at all running backs who finished in the top 24 at least once, and then classify them as either low-, medium-, or high-mileage as above. But then let's throw out any low- or medium-mileage back who was in the top 24 only once. So we're comparing low-mileage backs who finished in the top 24 at least twice to high-mileage backs who finished in the top 24
at least once

Mileage N RshAfter
Low 29 497.9
Medium 40 470.5
High 70 656.3

Still the high-pre-age-28-mileage backs had the longest post-age-28 careers.

This design helps to minimize some of the concerns with the earlier studies, but it has problems of its own. In particular, the group of backs who made the top 24 at least once is pretty large and contains a lot of fringe types. This lets in a lot of guys with low mileage, which drives the "high-mileage" cutoff down to a point where it's not really high-mileage in an absolute sense. In other words, the categories might more properly be called super low, low, and other instead of low, medium, and high.