DeMarco Murray embodies the fragility of the NFL life cycle

The life cycle of a professional football career can move at warp speed. One year, you're a hero and creating highlights that spread across America's televisions every Sunday. The next, you're disposed of and only seen on NFL Films archive footage.

Few players illustrate that better than running back DeMarco Murray, who retired after seven uneven years on Friday.

Being an NFL running back is often a maddening, taxing role that can go unappreciated, and the job routinely becomes expendable. Murray didn't enjoy the fruits of instant stardom after being selected in the third round of the 2011 draft and slotted into the third spot on the Dallas Cowboys' depth chart.

After spending the first half of his rookie year tethered to the bench, Murray finally made the most of his opportunities, rushing for 897 yards on 5.5 yards per carry. In most professions, that early success would be enough to earn some job security. But NFL running backs can't just be ordinary.

A foot injury limited his sophomore season to 10 games, but then Murray finally approached stardom with a 1,121-yard campaign in 2013. He submitted his magnum opus in 2014, winning the rushing title and Offensive Player of the Year Award after running for 1,845 yards and 13 touchdowns, adding 57 receptions for 416 yards.

Murray established himself as one of the faces of the Dallas Cowboys, a status that almost transcends football given the franchise's global popularity and billing as "America's Team." What more could you ask for in American sports?

Unbeknownst to Murray and Cowboys fans at the time, that was as good as it got for the running back, with his star rising then collapsing in rapid succession.

Conventional wisdom dictates that most teams in any sport typically want to retain the highest-producing players on the roster. But football's conventions are much different, and weeks after Murray finished his dream season the Cowboys let him walk as a free agent.

He left for the arch-rival Philadelphia Eagles. Few could fault Murray for wanting to exact revenge on the Cowboys, but his time with the Eagles was a doomed marriage from the start. He swiftly found redemption with the Tennessee Titans the following year, culminating in his third and final Pro Bowl season in 2016.

Murray's final NFL campaign was a quiet affair by his standards when he rushed for 659 yards on 184 carries (3.6 yards per carry). It became apparent the Titans were focusing on developing second-year pro Derrick Henry. After drawing little interest as a free agent throughout the spring and summer, it's obvious Murray isn't in demand.

Football is a cruel game for running backs, a position that takes violent collisions regularly. And now Murray's reward is a single rushing season that ranks third in the past decade.

Reaching the NFL is a nearly impossible quest, let alone remaining in the league for seven years. Murray's brief stardom should serve as an example for running backs such as Le'Veon Bell. He's demanding a pay raise, and is hearing the football culture at large frequently dismiss his requests as arrogance.

Murray should be remembered positively, and his quick career arch is a lesson to a young cohort of running backs now seen as the faces of the NFL, which includes Bell, Ezekiel Elliott, David Johnson, and Todd Gurley, all of whom have overcome major injuries.

They all need to enjoy the present for what it's worth, while still securing a payday before it disappears into the abyss.