As we reach the midpoint of the season, it's time to focus in on the ground attack for all 32 NFL rosters. Through eight weeks of play, which teams field the best running back units? Here we rank the league's backfields from top to bottom.

1. Pittsburgh Steelers

Key contributors: Le’Veon Bell, DeAngelo Williams

Le’Veon Bell is still the gold-standard for the running back position in the NFL. Over the last three seasons, he’s averaging 2.85 yards after contact per attempt, including a ridiculous 3.7 over 69 carries this season. Bell also had just a single fumble over that span, making him one of the most-secure options in the NFL.

2. Arizona Cardinals

Key contributors: David Johnson

If Le’Veon Bell is the NFL's 1a. running back, then that makes David Johnson 1b. The second-year player’s skill-set is so similar to Bell’s that it’s uncanny. Others may match his production on the ground this year, but no one is even close to Johnson when you add in his receiving prowess. He already has 1,112 yards from scrimmage, while no one else has over 1,000. Johnson's 46 combined missed tackles on handoffs and receptions are 14 better than the RB in second place.

3. Tampa Bay Buccaneers

Key contributors: Doug Martin, Jacquizz Rodgers

This is assuming full health for Doug Martin, which has been a big if over the course of his career. When he's at 100 percent, though, Martin has been a top-tier running back. Martin was the highest-graded runner in our system a season ago, and in Week 1, he broke seven tackles on 18 attempts. He’s fairly close to returning, but even with him out, it’s not as if the Bucs have been hurting with Jacquizz Rodgers running the rock. The journeyman is ninth in PFF's elusive rating metric, and is averaging 4.5 yards per carry.

4. Buffalo Bills

Key contributors: LeSean McCoy

LeSean McCoy had a couple of down years by his standards after his dominant 2013 season; he was freelancing far more than he needed to be with the impressive blocking he received in Buffalo and Philadelphia the past two seasons. Now McCoy's striking a better balance, and it’s shown in his stats. He already has 21 broken tackles (fourth-most in the NFL) after breaking 34 all of last season. McCoy also leads the league with 13 carries of 15 or more yards so far.

5. Dallas Cowboys

Key contributors: Ezekiel Ellott

There hasn’t been a noticeable change in the quality of run blocking from last year to now, the only difference is the massive upgrade from Darren McFadden to Ezekiel Elliott. All that offensive line needed was a running back with vision and decisiveness in his cuts; Elliott has been just that, and more. The rookie’s 473 yards after contact on the year are 44 more than the next-closest back.

6. Tennessee Titans

Key contributors: DeMarco Murray, Derrick Henry

What we thought was going to be a two-headed monster in the backfield has ultimately turned into the DeMarco Murray show. It’s quite amazing how much better Murray is running with the quarterback under center than from a shotgun position. Getting a head of steam rolling straight downhill makes his patented bounce out that much deadlier; Murray has already gained 469 yards on 64 runs that hit off the edge. Last season, he only gained 231 yards on 73 such carries.

7. Miami Dolphins

Key contributors: Jay Ajayi

When he’s been handed the ball this season, there’s been no more impressive running back than Jay Ajayi. Truthfully it’s not even debatable. In his last two games, Ajayi has 54 carries for 418 yards, 12 missed tackles forced, and 277 yards after contact. Only 18 running backs have more yards after contact on the whole season. The only question is, where does he go from here? Ajayi graded out extremely well as a rookie also, but still has only 134 carries in his NFL career.

8. Atlanta Falcons

Key contributors: Devonta Freeman, Tevin Coleman

Devonta Freeman has always been a solid, if unspectacular, starter, but the emergence of Tevin Coleman as a threat in the passing game pushes the Falcons into the top 10 on this list. Coleman’s 3.42 yards per route run is more than a full yard better than the next best running back so far this season. He’ll likely cool off at some point, but early on, the Falcons have done a great job getting both involved.

9. Cincinnati Bengals

Key contributors: Jeremy Hill, Giovani Bernard

I’m not sure I’d consider either Jeremy Hill or Giovani Bernard top-10 backs individually, but put them together and their sum sneaks them to No. 9. Their complementary styles allow Cincinnati to employ each situationally; the result is a top-five receiving grade from Bernard, and a top-20 rushing grade from Hill.

10. Houston Texans

Key contributors: Lamar Miller

Lamar Miller has been hit-and-miss so far this year, but the track record is there for a turnaround. He’s had a top-10 rushing grade each of the past two seasons, but has seen that fall in Houston. Miller was always a back who thrived on spread runs where he was afforded space to work with, and the Texans have asked him to be a more traditional between-the-tackles runner. Hopefully we see some changes in Houston that allow a return to form.

11. Seattle Seahawks

Key contributors: Christine Michael

It’s unfortunate that the Christine Michael hype-train finally reached full speed at the exact same time Seattle's O-line production came to a complete halt. The fourth-year back has been extremely impressive, and not only with his running ability. He’s also been one of the best pass-protecting running backs, with two pressures allowed in 42 pass-blocking snaps.

12. San Diego Chargers

Key contributors: Melvin Gordon

Even with a fully-healthy unit, San Diego still owns the lowest-graded run-blocking offensive line for the second straight season. That has to be considered when evaluating Melvin Gordon’s performance over the past two seasons. He’s one of the few running backs on here still that handles a full workload, seeing the field on all three downs. What's more, he’s been successful in that role, with above-average grades as a pass-catcher, pass-protector, and runner.

13. Cleveland Browns

Key contributors: Isaiah Crowell, Duke Johnson

Cleveland's running back situation is similar to that of Cincinnati's, albeit less-proven. Isaiah Crowell takes the bulk of the carries, while Duke Johnson gets change-of-pace work and passing situations. So far this season, they’ve fieled one of the most formidable rushing attacks in the NFL. Both are in the top-15 league-wide for elusive rating.

14. Kansas City Chiefs

Key contributors: Spencer Ware, Charcandrick West

The Chiefs may be without Jamaal Charles, but they really haven’t missed a beat on the ground with Spencer Ware. The fourth-year running back doesn’t even have 200 career carries to his name, but is averaging over 5 yards per carry on them. What’s been most impressive, though, is his production as a receiver this year. Ware is second in yards per route run (2.35), but almost everyone else in the top-10 is a third-down back. Among full-time RBs, he’s first—over half a yard better than the second-best back.

15. Carolina Panthers

Key contributors: Jonathan Stewart, Mike Tolbert

Jonathan Stewart can’t seem to stay on the field this season, and it’s reasonable to wonder if he’ll be the same player down the stretch after the sheer buildup of injuries. He hasn't yet reached the dreaded 30 plateau, but at 29 years old, he’s still likely slowing down. Stewart has earned a top-10 rushing grade in each of the past two seasons, though, so I’m not willing to write him off yet.

16. Los Angeles Rams

Key contributors: Todd Gurley

One can make all the excuses in the world about Todd Gurley’s offensive line, but at some point, the onus falls upon the running back. Gurley hasn’t been nearly as decisive in his reads as he was a season ago, and is pattering his feet in the backfield far too often. There's no doubt that the talent is still there, but Gurley is currently in a funk.

17. Chicago Bears

Key contributors: Jordan Howard

I’ll admit that some of my pre-draft evaluation of rookie Jordan Howard is creeping into my ranking here. Through 99 carries as a pro, though, it’s difficult not to be impressed with the fifth-round pick. The former Hoosier already has the fifth-most broken tackles on the ground (20), a figure that leads all rookies. What always impressed me, though, was Howard's vision, and I think that’s easily the biggest reason he’s been far more productive than the other backs the Bears have cycled through.

18. New England Patriots

Key contributors: LeGarrette Blount, James White

LeGarrette Blount’s stats may never look great because of the situations in which he runs the ball for the Patriots, but for what they ask him to do, he is perfect. The Patriots need a legitimate pile-mover to influence defenders when they bring in their ultra-heavy packages to try and punch defenses in the mouth. Blount has done just that, breaking 24 tackles this season and scoring nine touchdowns.

19. Baltimore Ravens

Key contributors: Terrance West

The lightbulb has finally turned on for Baltimore's Terrance West, and he’s been running extremely well behind a hodgepodge offensive line so far this year. Physically-speaking, he’s always been one of the most impressive backs in the NFL—he simply needed to learn the nuances of the position. Since West started seeing the bulk of the Ravens' snaps in Week 4, he has been the seventh-highest-graded RB in the NFL.

20. Oakland Raiders

Key contributors: Latavius Murray, DeAndre Washington, Jalen Richard

For all the love that the Cowboys ‘offensive line has gotten so far this year, it’s the Raiders who top our grading in run blocking. All three running backs have been effective statistically when given the chance, yet all three grade out around average. They have 14 combined broken tackles on 156 carries, which is one of the lower rates in the NFL.

21. New Orleans Saints

Key contributors: Mark Ingram, Tim Hightower

Mark Ingram to the Saints felt like an odd fit when they drafted him, and to this day, it still feels like he’s a bit out of place. New Orleans is a spread team that all of a sudden packs everyone in tight and wants to run the ball downhill. He’s competent at that, but doesn’t afford them much in the way of a weapon out of the backfield for a pass-heavy team. He can be effective after the catch on swing routes, and judging by his 18 broken tackles on 50 catches a season ago, he’s not the type of receiver that can beat coverage.

22. San Francisco 49ers

Key contributors: Carlos Hyde

Carlos Hyde teases greatness at times, but can’t seem to stay on the field long enough to sustain it. The fact of the matter is, Hyde now has 307 carries for his career and is averaging 4.0 yards per carry on them. He does have a ridiculous 73 broken tackles over that span, but at some point, it has to translate to production, or else he’s just a better version of Trent Richardson.

23. Jacksonville Jaguars

Key contributors: T.J. Yeldon, Chris Ivory

This group is far more talented they've demonstrated so far this season, but it’s hard to even put them this high at the moment. Chris Ivory looks like a shell of his former self, with the lowest elusive rating in the entire NFL this season, and three fumbles already. T.J. Yeldon was our second-highest graded rookie runner a season ago, but he too has gone backwards. His longest carry of the season is just 15 yards.

24. Philadelphia Eagles

Key contributors: Darren Sproles, Ryan Mathews

Darren Sproles agelessness really needs more attention than it’s getting at this point. He’s 33 years old and just broke six tackles on 15 carries against the Cowboys. Unfortunately, he’s still not a guy you’re going to give a full workload to, and Ryan Mathews has been generally ineffective as the lead back.

25. Indianapolis Colts

Key contributors: Frank Gore

You know what you’re getting with Frank Gore at this point, and it’s a back who’ll get what’s blocked, and not much more. That can help get your offense in favorable down-and-distances, but it’s not going to force defenses to worry about the run. That’s why he can still average 4.2 yards per attempt with a season long run of only 22 yards.

26. Detroit Lions

Key contributors: Theo Riddick

Theo Riddick is an odd player to slot on this list. If he were in a heavy-formation, run-first team like Tennessee, he’d be a terrible fit. Yet in a pass-first spread team like the Lions, he’s still a dangerous weapon. Riddick’s not the guy I want running when the defense knows the Lions are going to run, because his vision is iffy and he’s not a guy who’s going to drop his pads and deliver a blow. I can count the number of running backs that are tougher for linebackers to cover on one hand, though and that adds a lot of value to the Detroit offense.

27. Washington Redskins

Key contributors: Matt Jones, Chris Thompson

Matt Jones has looked much better in year two than he did as a rookie, except for the whole holding-onto-the ball thing, which I’m told is important. Jones’ four fumbles lead the position and put in question his status as the lead back. Still, though, much of his production is due to an absurdly-good offensive line, as Jones has been the fifth-least elusive back in the NFL.

28. Denver Broncos

Key contributors: Devontae Booker

Another ranking where, due to injury, I’m forced to throw my hands up and take a stab in the dark. Devontae Booker has 70 carries to his name, and while he’s looked better than the 28th-best running back in the league so far on those carries, it’s still such a small sample size. He was the 103rd player on our final draft board last spring.

29. New York Jets

Key contributors: Matt Forte, Bilal Powell

Matt Forte may still be a viable fantasy running back, but he’s doing the Jets no favors with his play this year. He’s almost an exact clone of Frank Gore at this point, though Forte is a little less-decisive in the backfield. He owns the fourth-worst elusive rating in the NFL this season, and has already dropped three passes as a receiver.

30. Green Bay Packers

Key contributors: Ty Montgomery

It's kind of difficult to slot a team into running back rankings when they currently don't have one, so the Packers get tossed in here. Wide receiver Ty Montgomery looks as though he may be the guy, but he hasn’t played the position since high school. As many times as I’ve said I don’t know what to expect from a guy going forward because of his limited touches, that is truly the case with Montgomery. He has 56 carries over the last six seasons.

31. New York Giants

Key contributors: Rashad Jennings, Bobby Rainey

The fact that the Giants are ranked below a team with a wide receiver starting at running back tells you all you need to know about how their backs have performed this year. Rashad Jennings is all but done at 31 years old, yet he still sees the bulk of the touches. His 1.7 yards after contact per attempt is dead last for any back with at least 50 carries this season. The only reason the Giants aren’t 32nd is because Bobby Rainey at least offers something as a receiver.

32. Minnesota Vikings

Key contributors: Matt Asiata, Jerick McKinnon

Blame the offensive line all you want, the guys running behind them own their fair share of the scrutiny for the Vikings' non-existent rushing attack. Matt Asiata is averaging 1.8 yards after contact per attempt, and is basically a glorified fullback with his running style. Jerick McKinnon at least offers some athleticism, but it hasn't translated to any sort of production as a receiver, where he’s averaging 3.6 yards per catch.