It always comes back to the running back. The National Football League has tried every which way to Sunday to eradicate the running back from its game plans and offensive schemes, but those Air Raid-oriented offensive coordinators just haven’t been able to give the little guys the boot yet. For all the 4,000-yard or 40 touchdown passing seasons for quarterbacks, we still are fixated on offensive balance and versatility. We will never get the image out of our heads of Russell Wilson throwing a Super Bowl-losing interception on the goal line, while elite running back Marshawn Lynch stood idly by, the decision and power taken out of his hands.

The running back might be the NFL version of the cockroach: resilient, indestructible, and weirdly omnipresent in a world that doesn’t like them. Yep, either a cockroach or a Twinkie.

That lovely analogy aside, the running back is still very important to the landscape of the NFL and to fantasy football, yet this position is still one of the few we don’t fully understand. For example, what is the relationship between talent and situation when it comes to production?

One of the things that has been discussed at length is the career arc for a running back. Where does the production drop-off happen? How long can they be effective in the league? Does age have anything to do with this, or is it just experience? With more and more emphasis on age in contracts and scouting, this becomes very important to understand.

La Peste

Running backs are bizarre creatures. They are highly needed and highly regarded until it comes time to value them in the market or during the draft. One of my favorite quotes in all of sports comes from former reliever for baseball’s Cleveland Indians, Jim Kern: "Isn't it amazing that we're worth so much on the trading block and worth so little when we talk salary with the general manager?"

This sentiment especially holds true for the running back in the NFL. The Minnesota Vikings paid star back Adrian Peterson $96 million in 2011 to play for the next seven years with $36 million guaranteed. Now, going into his age 30 season, they’re considering completely cutting him. The other option is trading him, but apparently their asking price is still far too high for any team in the league to remotely consider it. Part of his fluctuating value has nothing to do with his play on the field -- we know that -- but a great deal of it has to do with Peterson’s age and the $32 million he will be owed after age 30.

This is our general running back bias line: we believe that for some reason, running backs tend to drop in production after age 30. But is that entirely true? What determines the course of a running back’s career path?

L’Étranger

In order to examine this question, we turn to our good friend, Net Expected Points (NEP), our signature metric here at numberFire. NEP is a method of assigning context and meaning to the in-a-vacuum box score stats, which don’t address the most important value in football: how a player helps his team score points and win. For more information on NEP, check out the explanation in our glossary.

I plotted out the career Total NEP values (NEP gained from both rushing and receiving) for every running back drafted since 2000, as well as assigning their ages at time of being drafted, their overall selection, and draft round.

In order to figure out what a running back career looks like, the first thing we can look at is a map of average NEP production by age. The table below shows the averages of production for each age year of a player. What do we find?

Well, if we were to subscribe solely to an age-based hypothesis, it appears that a running back’s prime year is solely his age 20 season, and either 22 or 25 is their real drop-off in value. It actually appears that if a running back makes it to their age-30 season, they sustain generally the same amount of value into their post-30 years. The problem is that only 20 backs out of a sample size of 235 (8.47%) have even reached their age-30 season, likely because they’re very good.

Age seems to be a fairly inconclusive method of measuring career sustainability.

L’Homme Révolté

What if we looked at not age, but career years in the league? How would players’ NEP arcs appear based on a wear-and-tear idea, instead of an arbitrary aging curve? The table below shows this same NEP data represented in terms of the average NEP of running backs by league experience year. Is there a clearer pattern here?

It’s a little bit easier to visualize this in graph form, but we can see a clear arc from the table. After a usually slow Year 1, running backs tend to explode in their Year 2 and sustain this NEP production into Year 3. The first dip in the average running back’s production comes in Year 4 of their league experience, but this is another plateau that doesn’t appear to drop off until Year 7, and the Total NEP doesn’t go negative until Year 9.

Interestingly, most running backs enter the league around the average age of 21 or 22, and the drop-off to near-worthlessness in NEP production seems to occur right around Years 7 to 9. Do you see how this fits? The average NFL running back seems to fall off the table right around age 28 to 31. It seems our perception isn’t so off, but a strict age recommendation doesn’t seem to fit the reality.

Instead, we should be wary of players getting into their 7th to 9th years of NFL experience; they often won’t produce like we hope. There are obvious exceptions, Marshawn Lynch and Matt Forte this past year being two such cases, and the same with late-career Brian Westbrook of the Eagles and LaDainian Tomlinson.

However, this is the “typical” course of a career, and we should take advantage of this knowledge -- especially in dynasty fantasy football leagues.

For example, in one dynasty this offseason, I traded Forte for a first-round pick, a second-round pick, and Theo Riddick. Forte, entering his Year 8 of NFL experience in 2015, likely will not have a better season than his 2014 campaign in the future, at least according to the numbers.

This data just confirms our gut calls, and that in and of itself is important. Don’t devalue running backs entirely, but make the most of your fantasy assets. This is one way to do that.