Stephen Dubner

Overall, the 2011 CBA was a lucrative affair for the players.

Their share of league revenues rose from 42% to 47%.

But that agreement also came with some restrictions for rookies.

Before 2011, a drafted player could freely negotiate a contract with the team that chose him.

This led to some bad deals for teams when the player didn't play well or got hurt.

The 2011 agreement created a rookie wage scale that set contract terms based on draft order.

It also mandated a four-year contract with a cost-controlled fifth-year option that their team could exercise.

This structure is still in place today, and that's what Robert Turbin is talking about when he tells Roland Fryer that the team has control of you for five years.

For some positions in football, including quarterback, a player is just coming into his prime at age 27.

That is not the case for running backs.

If you go back 20 years, the average career length for an NFL running back was around five and a half years.

That number started dropping right around the 2011 collective bargaining agreement.

And today, the average length is around two and a half years.

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.