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Fantasy Football: The Myth of Overworked Running Backs

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Jonathan Bales

Which "fantasy" football do you prefer--analytical, stat-driven research as it relates to the NFL, or "Fantasy Girl" and "The Blonde Side" author Amber Leigh? Luckily, we have both for you.

Note:  This is a two-page entry.

Every year during my fantasy drafts (I would say the exact number of leagues in which I participated last year if I wasn’t so embarrassed about the number–hint: I can’t even count them all with my fingers and toes), I hear a variety of fantasy football “truisms” thrown out following the selection of certain players.

“Wide receivers always break out in their third year.”

“Don’t draft a kicker until the last round.”

And perhaps most frequently, “Running backs are never the same the year following a season of 370 (or any other arbitrary number) touches.”

It is this last notion which will be the subject of this post.  There have already been some informative studies produced on the decline of running backs following a season of heavy work, not the least interesting of which can be found here.

Before delving into the results, it is critical to once again rehash the importance of the correlation/causation distinction.  In our article on the importance (or lack thereof) of offseason workouts, we wrote:

Both of these notions–running the ball and having a good coach–are onlycorrelated to winning.  Correlation does not equate to causation. For example, intelligence is rather strongly correlated to shoe size.  Does possessing big feet make you smarter?  Of course not, but people with big feet are generally older, and older people tend to be more intelligent than children (although that is unfortunately not always the case).

Nonetheless, we only notice the presence of these characteristics when it is too late–they have no predictive power.

With the distinction between correlation and causation in the back of our minds, let’s examine the stats regarding a running back’s touches and his performance the following season.

Football Outsiders (a terrific site, by the way) completed a study on the workload of running backs and summed up their results as follows:

A running back with 370 or more carries during the regular season will usually suffer either a major injury or a loss of effectiveness the following year, unless he is named Eric Dickerson.

Terrell Davis, Jamal Anderson, and Edgerrin James all blew out their knees.  Earl Campbell, Jamal Lewis, and Eddie George went from legendary powerhouses to plodding, replacement-level players.  Shaun Alexander struggled with foot injuries, and Curtis Martin had to retire.  This is what happens when a running back is overworked to the point of having at least 370 carries during the regular season.

Is 370 carries really a magical number by which we can judge the future effectiveness of a running back?  It is certainly true that a running back coming off of a season with a heavy workload is more likely to be less effective and more likely to get injured than was the case in the prior season–but is this truly the result of the high number of touches, or is it due to something else?

The truth is that, while the statistics do point to a decrease in effectiveness and an increase in rate of injury following a heavy-workload season, these numbers are both insignificant and irrelevant.

It is easy to gather "significant" results if cut-off points are chosen after reviewing the results. The mark of a good theory, however, is its predictive power. Using a player's workload from the previous season (particularly when an arbitrary number of carries is chosen after the fact) has little predictive power as it relates to his production the following season.

The key is in a statistical term known as ‘regression toward the mean.’ Mathematics is a beautiful thing.  Given a large enough sample size, numbers always win.  Flip a coin 10 times, for example, and the number of heads you obtain could realistically be anywhere from one to 10.  Flip it 100 times, though, and you are very unlikely to acquire more than 70% of either heads or tails.  Flip it 1,000 times, and it is a virtual certainty that you will have flipped no more than 60% of heads or tails (and much more likely, less than 55%).

This predictability through which the universe manifests itself is not irrelevant to football.  Two-point conversion rates and onside kick recovery percentages, for example, remain relatively stable from year to year.  There may be blips in the data from time to time, but the overall statistics always (always!) regress back toward the mean.

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6 Responses to Fantasy Football: The Myth of Overworked Running Backs

  1. Vince Grey says:

    I see your point, and your math, but I have to disagree with your conclusion. Based on your example, there’s no reason at all why a great RB should decline once he hits his 30’s and yet the vast majority do just that. Technically, by purely mathematical standards, the number 30 should have no real bearing, but the actual visual evidence says otherwise.

    On another point, I don’t see the number of 370 being an absolute, but merely a numerical reference point. In other words, I’m virtually certain the author wasn’t saying that a RB getting 371 carries is all but doomed the next year, while the one getting 368 will be likely be just fine.

  2. Good comment VInce. I actually agree with you on age…I think it is MUCH more of a factor in a running back’s production than touches. Now of course the age 30, just like the 370 carry number, is by no means absolute (as you point out).

    However, I think the correlation between age and decreased production is due to a causal relationship. In the case of age/production, there does seem to be a significant relationship between the two that is apparent no matter how we slice the data. In the case of touches/production, however, a bit of statistical trickery and ignorance of regression toward the mean is needed.

    Perhaps a study on the relationship between age and production is in order?

  3. Vince Grey says:

    There’s another point that I left off, and that is that both authors completely ignored the number of receptions and blocking. While I’ll concede that one could argue that a pass reception doesn’t have the same “impact” to a RB as a carry, it’s certainly close enough, (Say, 2/3 or 3/4 if you want to be picky) and certainly blocking has as much impact or more.

    What also must be factored in is the style of the runner. Earl Campbell was a power back slasher who hit, and got hit, hard, A LOT. OTOH, I rarely saw Emmitt Smith take a direct hard hit.

  4. Of course every situation is different, but to make any sort of grand conclusions, we must lump at least some players together who are not completely similar. This would include pass-catchers with non-pass-catchers and RBs who took bit shots with those that didn’t. You are right, though, that every situation should be treated on an individual basis.

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