In his latest First and 10, Mark Maske touched on the importance of running backs in today’s NFL. There were two passages that struck me:

The takeaway from all of that is that, yes, the standout running backs still matter and they come with a very considerable price tag. But they generally don’t matter as much as those who throw and catch passes, and they don’t matter for all that long.
This past week showed that there are running backs who remain game-changing players in this league. But it also showed that the shelf life is comparatively brief for players at that position, even the great ones. They are subject to being pointed toward the door, or even shoved out of it, at practically any time in a way that happens less frequently and less abruptly to top quarterbacks and standout wide receivers.

Running backs have been phased out of the league for some time. It started as a subtle shift, but has now grown to a clear preference for passing the ball. For example, the last time the league saw teams with equal parts rushing and passing attempts was in 1983. And starting with 2008, the divide continues to grow.

As a result, quarterbacks are more integral to winning than either running backs or wide receivers. Below shows how much. Each position player is ranked according to his 2104 win probability added, which simply measures the impact of each play toward winning and losing. As you can see, the top five quarterbacks per this metric vastly outweigh their comparables at running backs and wide receiver and continue to do so for the top 15 at the position. It’s not even close.

Perhaps this explains the larger-than-expected number of teams interested in signing Brian Hoyer as their quarterback. It also explains why running backs have such a short shelf life, one that is getting shorter with each passing year. Below is the average tenure of running backs, quarterbacks and wide receivers in the year they were no longer active. The dotted lines are five-year moving averages to help smooth out the curves. As you can see, passers (and with them, receivers) are on the rise while rushers are on the decline. From 2010 to 2014, the average tenure of a running back no longer in the league was 5.2 years, compared with 7.2 for quarterbacks and 6.4 for receivers. That’s almost a year difference from the period encompassing 2001 to 2005.

Here is how the attrition looks through the lens of Approximate Value, Doug Drinen’s method of putting a single numerical value on any player’s season, at any position, from any year. The simplest way to look at AV is higher is better and anything more than a 10 is a Pro Bowl-caliber season. DeMarco Murray topped the AV leader board among rushers last season with 19.

Running backs that averaged over 10 AV per 16 games and ended their career between 2010 and 2014 played 9.5 seasons, on average. That same class of rushers who stopped playing between 1995 and 1999 played an average of 13 seasons.

But this isn’t happening “less frequently and less abruptly to top quarterbacks and standout wide receivers.” In fact, quarterbacks who average more than 10 AV per 16 games over their career have a life span close to rushers of the same caliber. But wide receivers of this ilk have seen their time on the field increase over the past five years.

In other words, game-changing receivers are in the league two more years than they were in the previous five-year period and three years more than star passers and rushers.

At some point running backs will actually become undervalued and a team will use Moneyball-esque strategies to gain a significant edge on their competition. But for now, don’t run out and buy a jersey if your team signs that prized free agent running back.