Stephen Dubner

Let's hear now from another former running back, Robert Smith.

Like Robert Turbin, Smith played for eight years.

All of his were with the Minnesota Vikings.

Smith retired after the 2000 season.

Today, Smith calls NFL and college games for Fox Sports.

His reverence for the running back position goes deep.

Those occasional bursts of excitement are, of course, offset by thousands of hours of training and by the physical punishment.

Robert Smith had a lot of reasons to walk away, a lot of things beyond football that excited him.

He is an amateur astronomer, a prolific reader, and in addition to his broadcasting duties, he is working on a health and wellness startup, plus which he made good money as a younger man.

His final contract paid him $25 million over five years.

In his last season, the best of his career, he ranked second in the NFL in rushing yards.

But it was clear by then that running back money was drying up.

Every team has a league imposed salary cap, and they're constantly trying to figure out which players they can give less money to in order to give more money to the players they think they cannot win without.

And running backs had fallen off the cannot win without list.

Over the past few decades, NFL revenues have more than doubled to about $20 billion a year.

Since players get a percentage share of revenues, that means the overall player pool has also more than doubled.

But running backs have barely shared in that gain.

The pay for running backs and fullbacks over the past two decades has risen around 11%.

For all other offensive positions, salaries have risen at least 90%.

If you don't believe me, just ask an agent.