In the NFL, only kickers and punters get paid less than running backs. Offensive linemen, linebackers, and even tight ends make more than one of the league’s marquee positions. That seems curious, seeing as some of the sexiest names in the league line up in the backfield, but those players typically don’t last long. Running back careers have become so short that teams often refuse to invest in the position. Look no further than DeMarco Murray, who, three years after being one of the best players in football, retired on Friday.

Murray called it a career after seven seasons in which he racked up 9,339 yards from scrimmage, 55 touchdowns, three Pro Bowl appearances, and one solid contract from a team that almost instantly regretted signing it. In 2014, Murray was the best running back in football, and led the league with more than 1,800 rushing yards and 13 touchdowns behind Dallas’ talented offensive line. And he was due for a new contract at season’s end. The Cowboys offered him a four-year, $24 million deal, but Murray spurned them and went to the divisional rival Eagles on a five-year, $42 million contract.

It was a good deal for Murray. The $18 million guaranteed at signing was the third-highest for a running back at that time behind only Arian Foster and LeSean McCoy. But in his first season in Philadelphia, Murray disappointed, rushing for just 702 yards on 3.6 yards per carry. The then-27-year-old was so mediocre that, just one year after being one of the most important offensive weapons in the league, the Eagles traded him to the Titans for a fourth-round pick swap. Tennessee was the only team willing to take a chance on a player who just one year earlier was the AP Offensive Player of the Year.

After a brief resurgence in his first season with Tennessee (Murray rushed for 1,287 yards for the Titans in 2016), he faltered last year, with career lows in rushing yards (659) and yards per carry (3.6). The Titans cut him in March, saving $6.5 million against the salary cap, and four months later, no team had signed him. The Dolphins worked him out, but serious interest never seemed to emerge. And now, at age 30, Murray is hanging up his cleats.

Murray is a perfect example of why NFL teams don’t want to hand out big deals to running backs. After being drafted in the third round in 2011, he gave the Cowboys 4,526 rushing yards (4.8 per clip), 1,200 receiving yards, and 29 touchdowns through four seasons. During that stretch he was paid just $3.65 million. Then, when it came time to cash in on his rookie-contract production, the Cowboys lowballed him and let him walk. It’s ugly, doing that to a superstar. It is, also, given the league’s economics, the right business decision for the team.

Murray’s career arc—his immediate production and near-immediate decline after signing a real contract—has implications for some of the league’s current best backs. Le’Veon Bell is close to playing on the franchise tag for a second consecutive year as the Steelers waffle at giving him a long-term deal. Bell led the league in rushing attempts last year, and while he’s just 26, that was also the age Murray was in his All-Pro year. The Rams’ Todd Gurley is even younger—just shy of 24—but he sees the writing on the wall, and has been telling anyone who will listen this offseason that NFL players deserve fully guaranteed contracts. Gurley still has another two years left on his rookie deal, and after that he may be in the same franchise tag hell in which Bell has found himself. Arizona’s David Johnson has had virtually no traction in trying to get a new deal. And soon Ezekiel Elliott, Alvin Kamara, Kareem Hunt, Leonard Fournette, and even Saquon Barkley will likely find themselves in similar situations.

Running backs’ careers are too short for them to cash in—they’re the second-shortest in the league by position after wide receivers, per The Wall Street Journal, though elite-level wideouts certainly seem to last much longer than elite running backs. The first four or five seasons for a running back—when they’re tied up in bargain rookie deals—is generally the time they’re most valuable. Murray was able to cash in on one solid contract, and the Eagles were lucky just to move on from him when they did. If the Cowboys had given Murray the contract he wanted, it could have been a disaster for the long-term success of the team, and NFL franchises will no doubt take note. When it’s time to get paid, a rusher’s best years are often already behind them—and teams know that. For many players, that time is already here, and teams are going to look at what happened to Murray. Then they’ll do the same thing the Cowboys did: Lowball them, or let them walk.