As a Bears fan, watching the team struggle—and fail—to put up more than three points against the abysmal Kansas City Chiefs yesterday left me pondering all sorts of questions. But after Matt Forte, the team’s star running back, went down with a nasty-looking knee injury, the one that I spent the most time thinking about was whether Forte’s position is the worst one in all of sports.

During the NFL lockout this spring and summer, the battle was frequently characterized as “millionaires versus billionaires.” And that’s true, if you consider only the stars of the league. Tom Brady, Peyton Manning and Drew Brees—the three top-billed plaintiffs in the NFL Players Association antitrust lawsuit against the league—definitely fit that description. But the average NFL player makes a lot less than those guys—$770,000 a year, factoring in both the massive payouts for the superstars and the meager earnings of the practice squad players—and a running back like Forte, still on his rookie contract, earns less than that average ($555,000 for the 2011 season). That’s the same amount that Ravens starter Ray Rice earns, and slightly more than Eagles lone offensive bright spot Lesean McCoy and hope-of-the-Texans-franchise Arian Foster are signed for. Those four players could well be among the five best at their position this year, and not one of them makes the league average salary.

Those guys don’t even make $600,000 a year? They should put out a tip jar!

It’s hard to have much sympathy for the poor, poor NFL players who don’t even make a million dollars a year when Texans back Arian Foster still earns about fifteen times the average starting teacher’s salary in Houston. But a teacher’s career is expected to last more than three years—the average length of an NFL player’s time in the league—and there’s a well-oiled machine that tells pro-track players that the only thing that matters if they want to make it to the NFL is to dedicate themselves 100% to football. That means that acquiring skills for life after the league is considered tantamount to giving up on your dreams, for all but the most exceptional people who play the game at the highest level.

There are also factors that make the base salary a deceptive figure—agents and lawyers that take their slice, and friends and family for whom the player is financially responsible (or who see him as a potential meal ticket).

For a running back, that short earning window is significant. There are really only two possible outcomes on every play at the position: either you get hit, or you score a touchdown without ever being contacted by another player. One of those things happens a lot more often than the other. If the player stays in to block, he’s hit; if he takes the ball, he’s hit. Those hits add up, and for Forte—who suffered an MCL sprain yesterday—it can mean an injury that dramatically reduces his ability to ever get paid near the market value for the job of “starting NFL player.”

But for running backs, that market value is crashing. It’s not a coincidence that Forte, Foster, McCoy and Rice are all making less than the league average. The position is being treated as though it’s interchangeable—look at the success the Cowboys have had by churning through backs, dumping Marion Barber and Tashard Choice after the lockout ended and relying on Felix Jones and rookie DeMarco Murray to carry the ball (Jones makes just over $1 million on the year; Murray is earning $745,000).

And while a person can argue that this is just simple supply and demand—that a running back in the NFL isn’t worth paying a big contract to anymore—that just raises the question: Given the risk of injury and the absolute physical pummeling that even a healthy back takes every Sunday, is this the worst job in sports?

It’s either that or hockey enforcer.

After the lockout, Tennessee Titans running back Chris Johnson held out of training camp for weeks. As the leading rusher in the league since 2008, he was slated to make $1.065 million for the 2011 season, and he wanted a new contract. It took weeks, but he got it. After signing the deal, his production dropped dramatically—he averaged 2.8 yards per carry through the season’s first seven games, a number that would get him benched on any high school team in America no matter whose kid he was. Fans of the teams that Rice, Foster, McCoy and Forte play for cite Johnson as a reason why teams shouldn’t give a big payday to a player who holds out for more money.

But it’s hard, in light of what happened to Matt Forte’s knee, to give that view much credence. Forte is lucky—his injury looked like it could have been the NFL player’s death-knell, a torn ACL, but turned out to be a much less severe MCL sprain—but he’d be crazy to rush back out onto the field, having been reminded firsthand that any play can result in a life-changing injury, for the amount of money he’s making now.

Ultimately, it’s likely that the league and its backs are going to be at an impasse before long. Teams will continue to undervalue the position, and the best players at the pro level will hold out for better contracts. Some will get it, and a lot of them won’t (Clinton Portis, Tiki Barber and Larry Johnson are among the big-name backs who are currently out of work). But at the lower levels of the sport, there’ll be an impact, too: the most gifted runners might start looking at playing other positions, if the prospect of spending a few years in the pros as the lowest-paid starter on their team before suffering an injury doesn’t appeal to them. Former Longhorns tailback Henry Melton is now a starting defensive lineman for the Bears, and any great athlete can be versatile.

Matt Forte managed to avoid becoming a legendary cautionary tale yesterday. Here’s hoping that Arian Foster, Ray Rice and Lesean McCoy can do the same. But the NFL is going to have to figure out a fair market price for athletes of their caliber, or it’s hard to imagine there won’t be repercussions down the line. If you send the message that running backs aren’t worth paying for, the star players of the future are going to hear that, too.