When superstar running back Le’Veon Bell rejoins the Pittsburgh Steelers in preparation for the 2018 season — whenever that may be — he’ll have to get reacclimated to NFL life quickly. As part of a contract dispute, Bell has been training away from the team, reportedly planning to return just before the regular season begins. For most players, this would present an enormous challenge in preparation — but, then again, Bell isn’t most players.

For one thing, he’s done this before. Just last season, he followed a similar plan amid similar contractual friction — and all he did was generate 1,946 yards from scrimmage and earn first-team All-Pro honors. Beyond that, Bell also has a point to prove: As ESPN’s Adam Schefter tweeted in July, “Bell does not believe he should be paid as a RB; he believes he should be paid as an elite offensive weapon.” In a league where running backs are often viewed as disposable goods, Bell wants to transcend his position and be considered (and paid) in the same category as top quarterbacks. But can any running back — even a brilliant all-purpose one like Bell — ever be that valuable in an increasingly QB-centric sport?

Bell’s contract squabble is a direct reflection of the chasm between the market for an elite RB and the value Bell sees in himself. For the second consecutive year, Bell appears likely to enter the season signed under the franchise tag, and he would earn $14.5 million under the tag this year. For their part, the Steelers don’t seem willing to go any further than that as a yearly average in the long-term contracts they’ve offered to Bell, and that number is in line with the going rate for top ball carriers. Although Todd Gurley recently signed a record-breaking contract with the Rams that reflected the league’s growing reappreciation of RBs, the deal still pays only $14.4 million per year even if he plays it out to completion.

By comparison, the franchise tag value for quarterbacks is $23.2 million this season, with the top earners grabbing nearly $30 million. (The 49ers were even willing to give an average of $27.5 million to a QB with an extremely short track record.) For all the recent progress running backs have made, the NFL market still says that a top passer adds a lot more value than the guy he hands the ball off to. Is that warranted?

We can get a baseline for how much a star at each position affects his team by looking at what happens when he’s out. For instance, bookmakers will tend to move lines by as much as a touchdown when a Hall of Fame-caliber quarterback such as Aaron Rodgers is absent, while solid QBs like Russell Wilson trigger 4- to 5-point swings. When a top RB like Bell misses time, the oddsmakers will move the line only a half-point or so.

In practice, though, running backs might deserve a bit more credit. Although the sample of top players who missed significant time isn’t large, I culled the data at Pro-Football-Reference.com since the 1970 AFL-NFL merger for skill players who ranked among the top five at their respective positions in Approximate Value one season, then played six or fewer games the following season.

For the 20 quarterbacks in the sample, their team’s offensive Simple Rating System (SRS) score dipped by 4.7 points per game between the seasons with the top-five QB and without him.

How steep is the drop when a top QB is missing? Change in offensive Simple Rating System (OSRS) scores between seasons for NFL teams who lost a top-five quarterback, 1970-2017 Season w/ Player Season w/out Quarterback team Year AV team osrs Year team osrs Diff. in OSRS Andrew Luck IND 2016 16 +3.1 2017 -6.1 -9.2 Peyton Manning IND 2010 16 +3.7 2011 -6.0 -9.7 Tom Brady NE 2007 24 +15.9 2008 +2.3 -13.6 Carson Palmer CIN 2007 14 +1.6 2008 -6.9 -8.5 Michael Vick ATL 2006 15 -2.8 2007 -5.8 -3.0 Michael Vick ATL 2002 17 +3.5 2003 -2.0 -5.5 Steve Young SF 1998 19 +8.8 1999 -4.5 -13.3 Randall Cunningham MIN 1998 19 +13.2 1999 +5.2 -8.0 Dan Marino MIA 1992 15 +2.1 1993 +3.9 +1.8 Randall Cunningham PHI 1992 15 +4.8 1993 +0.7 -4.1 Randall Cunningham PHI 1990 19 +4.5 1991 -0.3 -4.8 Joe Montana SF 1990 14 +1.2 1991 +6.6 +5.4 Roger Staubach DAL 1979 14 +3.0 1980 +7.8 +4.8 Bert Jones BAL 1977 15 +3.6 1978 -2.8 -6.4 Jim Plunkett NE 1974 14 +6.6 1975 -2.3 -8.9 Joe Namath NYJ 1972 15 +4.7 1973 -1.5 -6.2 Roger Staubach DAL 1971 14 +8.3 1972 +3.4 -4.9 Bob Griese MIA 1971 15 +2.4 1972 +4.5 +2.1 John Brodie SF 1971 12 +2.4 1972 +4.9 +2.5 Sonny Jurgensen WAS 1970 15 +3.6 1971 -0.6 -4.2 Average 15.9 +4.7 +0.0 -4.7 Top-five status was determined according to Pro-Football-Reference.com’s Approximate Value. To qualify, a quarterback needed to play six or fewer games in the following season. Source: Pro-Football-Reference.com

Even in a small sample, that average fits in perfectly with Vegas’s conception of how important a top-level QB is to his team’s offense. For the 19 running backs in the sample, though, the effect was only slightly smaller — a dip of 4.2 points per game without a top RB, according to SRS.

What about when a top RB is missing? Change in offensive Simple Rating System (OSRS) scores between seasons for NFL teams who lost a top-five running back, 1970-2017 Season w/ Player Season w/out Running Back Team Year AV Team OSRS Year Team OSRS Diff. in OSRS David Johnson ARI 2016 15 +2.4 2017 -4.0 -6.4 Adrian Peterson MIN 2015 14 +1.1 2016 -2.6 -3.7 Le’Veon Bell PIT 2014 17 +4.4 2015 +5.1 +0.7 Knowshon Moreno DEN 2013 13 +14.1 2014 +9.2 -4.9 Doug Martin TB 2012 14 +1.3 2013 -2.9 -4.2 Maurice Jones-Drew JAX 2011 13 -7.1 2012 -8.1 -1.0 Tiki Barber NYG 2006 18 +1.2 2007 +2.8 +1.6 Edgerrin James IND 2000 21 +7.1 2001 +6.1 -1.0 Robert Smith MIN 2000 18 +4.3 2001 -0.8 -5.1 Ricky Watters SEA 2000 15 -1.4 2001 -1.4 +0.0 Terrell Davis DEN 1998 22 +9.5 1999 +1.0 -8.5 Jamal Anderson ATL 1998 19 +7.0 1999 -4.0 -11.0 Garrison Hearst SF 1998 18 +8.8 1999 -4.5 -13.3 Dalton Hilliard NOR 1989 15 +2.3 1990 -4.7 -7.0 Ickey Woods CIN 1988 13 +7.1 1989 +4.6 -2.5 William Andrews ATL 1983 18 +2.9 1984 -3.7 -6.6 Curt Warner SEA 1983 15 +3.4 1984 +5.4 +2.0 Otis Armstrong DEN 1974 22 +3.4 1975 -2.7 -6.1 Ron Johnson NYG 1970 18 +1.9 1971 -1.7 -3.6 Average 16.7 +3.9 -0.4 -4.2 Top-five status was determined according to Pro-Football-Reference.com’s Approximate Value. To qualify, a running back needed to play six or fewer games in the following season. Source: Pro-Football-Reference.com

That drop-off is barely distinguishable from the one felt after a team loses a top QB. (Interestingly, Bell’s own Steelers were one of the few teams that didn’t feel the ill effects of losing a top RB: When he missed 10 games in 2015, the team improved from seventh in scoring to fourth.) The gap becomes a bit wider in favor of quarterbacks — from 0.5 points of SRS to 1.0 — if we look at results only since 1978, when NFL rule changes made passing much easier. That indicates the increased value of signal-callers, and the diminished importance of rushers, as the game has evolved. But even so, these numbers suggest that star running backs do add an important — and perhaps underappreciated — dimension to teams that is missed when they’re gone.

Bell isn’t your ordinary star running back, either. He’s arguably the league’s most dominant player when healthy, a rare dual threat as a runner and receiver who ranks as the NFL’s all-time leader in scrimmage yards per game. As far as RBs go, he is the closest we’ve seen to that mythical “elite offensive weapon” since the days of Marshall Faulk or LaDainian Tomlinson. And luckily for Bell, that archetype is exactly what a modern RB hoping to earn more money looks like. Although number-crunchers realized long ago that rushing is less efficient than passing — which eventually ate into RB salaries — the value of a multi-dimensional player like Bell isn’t cut-and-dried. Over the past five seasons, Bell is the only NFL player who moved the chains for more than 400 first downs (he had 411), and he did it in 17 percent fewer games than runner-up LeSean McCoy (who had “only” 385 first downs).

Of course, there are always plenty of hang-ups with giving huge paydays to running backs, even if they’re as productive as Bell has been. Running backs with 15-AV seasons — the number Bell has hit in each of his past three full campaigns — make the Super Bowl at a rate 15 percent less frequently than 15-AV quarterbacks do. Traditionally, running backs also tend to lose a lot of their value from Bell’s current age (26) onward — and it’s unclear how much the league’s recent shift toward receiving backs will actually affect workloads as it pertains to aging.

Plus, for all of Bell’s yardage, there’s also statistical evidence that the Steelers haven’t quite figured out how to fully harness him as that elite offensive weapon, at least in terms of maximizing his expected points added. As Eric Eager and George Chahrouri of ProFootballFocus noted, Pittsburgh got negative EPA (meaning its expected scoring went down) on Bell’s runs last season. And while the team’s EPA on passes intended for Bell made up for it, he tends not to be targeted as far downfield as other elite dual-threat RBs such as New Orleans’s Alvin Kamara, which limits the damage he can truly do as a receiver.

That last piece of the puzzle might be the most frustrating part for Bell’s value-based argument, because it largely comes down to scheme and deployment rather than talent or effort. As multi-purpose running backs become more in vogue across the league, cracking the code on how best to maximize their value is still a work in progress, and Bell’s next contract may come too soon for a player of his abilities to fully cash in.

Before Bell, Vikings quarterback Kirk Cousins was the only skill-position player ever to be franchise-tagged in consecutive seasons — and he eventually parlayed his situation into what was at the time the biggest contract in NFL history. But, of course, he was a quarterback. Only time — plus the ever-shifting RB market and Bell’s own performance this season — will tell whether Bell can dash into Cousins’s territory under the “elite offensive weapon” label, or merely settle for running-back money in the end.