Welcome back to the Rankings File, an ongoing spring and summer series rating the best and worst units in the NFL. This week, we examine defensive front sevens.

Why "front sevens" instead of breaking down defensive lines and linebackers in separate weeks? There are many reasons, starting with the simple fact that we can argue for hours about where a defensive end ends and an outside linebacker begins. Any rating of best defensive lines would be dominated by the four-man lines of 4-3 defenses, while linebackers in 3-4 would overwhelm their own "best of" lists. Then we have to worry about the hybrid defenses and "Leo" defenders. The final rankings would be full or arbitrary distinctions and a few silly results.

By rating front sevens in their entirety, we can brush off the 3-4/4-3 one gap/two gap distinctions and concern ourselves with the major duties of a defensive front: run defense, pass rush and defending short passes, particularly to running backs and tight ends. When sifting through the mountains of Football Outsiders statistics, I focused on various evaluations of success at stopping the run and chasing the quarterback, including Power Success (stopping goal-line and third-and-1 rushes), Stuffed Rate (percent of running backs stopped for no gain or a loss) and Adjusted Sack Rate (which accounts for pass attempts and other factors, including the quality of the opponent).

A few other statistical indicators got tossed into the stew. Broken tackle totals and rates were given some consideration. Football Outsiders also keeps track of the success opposing offenses have when throwing passes to running backs and tight ends, from completion rates and yardage on those plays to interceptions and third down conversions. The results are a handy indicator of whether a defense is doing a good job of covering backs and tight ends or perhaps generating such a massive pass rush that opponents must always keep those players into block.

After all the number crunching, Pro Bowlers, newcomers, departures and top prospects are tabulated. Established coaches who have kept a successful system in place for years get a little boost. Run the spreadsheet through some formulas and Presto! Offseason web content!

As with last week's offensive line ratings, only the top five, bottom five and five "worth mentioning" teams are ranked. The plan is to keep me from writing about middle-of-the-pack units week after week, and to prevent arguments about whether some team should rank ninth or 13th, even though splitting hairs that finely is impossible. If you read last week's comment session, you know that the argument prevention tactic backfired, but comment thread arguments can be more fun than articles anyway.

You are going to see a lot of NFC West at the top of this list, which should not surprise you. Just what order those NFC West teams arrive in, however, may be a bit of a shock.

The Five Best Defensive Front Sevens

1. St. Louis Rams

If all you know about the Rams front seven is that Michael Sam is trying to crack the depth chart, then you are missing out on the NFL's tastiest Defense Lover's Plus Pizza.

Here is what you need to know about last year's front four of Robert Quinn, Chris Long, Michael Brockers and Kendall Langford: they combined to make 196 plays, from sacks to run tackles to batted passes, which is a very high total for a defensive line. Opponents netted a total of 78.7 yards on those plays, including yards gained or lost before turnovers. So those four players accounted for 12.25 plays per game that amounted to 0.4 yards per play for the opponent. And that's before they hurry a quarterback into an incomplete pass or occupied blockers so the linebackers and safeties could go to work. Think of the Rams defensive line as starting each game with four three-and-outs that leave the opponent punting from about the 22-yard line, and you get a sense of their impact.

Just one more thing, Colombo: the Rams line got better in the draft. Aaron Donald was the best defensive tackle prospect on the board. He is short for an interior lineman, but it won't matter when he is standing between Quinn, Long and either Brockers or Langford. This is pure unblockability, as teams like the Saints learned last year, and that's before you get to a pair of rangy all-purpose linebackers named James Laurinaitis and Alec Ogletree.

Ogletree and Larinaitis combined for 19 passes defensed, helping to make the Rams the hardest defense in the NFL to complete passes to a tight end against. Of course, not many tight ends were running patterns when blockers needed so much help with Long and Quinn. And Ogletree forced six fumbles. This front seven is so good that it could almost sue the rest of the team for non-support: point and yardage totals against the Rams were incredibly misleading because the offense kept giving the ball back. If the rest of the Rams ever catch up to these guys, watch out.

2. Carolina Panthers

Subscribe to NFL Game Rewind, then invest a few hours re-watching the Panthers games against the Seahawks (a 12-7 loss) and the Niners (10-9 win in the regular season; 23-10 playoff loss that was close for two-plus quarters). You will see a Panthers team designed and poised to challenge the NFC's top two teams for years to come: ball control offense, outstanding defense, toughness on both sides of the ball.

You will not see that Panthers team this year, because their front office put in extra hours to screw everything up. But they were so busy gutting the receiving corps, secondary and offensive line that Dave Gettleman and Jerry Richardson never got around to the front seven. That's a good thing, because the Panthers' outstanding front seven is the only thing that will keep them competitive this year.

Luke Kuechly is one of the two best inside linebackers in the NFL right now, with Lavonte David of the Buccaneers jockeying for the title. Thomas Davis emerged from years of injuries to suddenly post a marvelous season last year. But the real stars of the defense are the front four, sometimes known as MonStrz Inc. Greg Hardy and Charles Johnson combined for 26 sacks and a whopping 46 quarterback hits last year. Star Lotulelei and Kawann Short did not provide much statistical production, but the two 2013 rookies occupied blockers so Kuechly could roam free. Free to play a more situational role, Dwan Edwards provided disruption in small doses.

Hardy has pending legal issues, but rookie Kony Ealy is in the fold as insurance, and A.J. Klein provides a situational penetrator behind veteran Chase Blackburn, giving the Panthers plenty of depth. The team will be counting on even more 10-9 victories this year than last year. This front seven can generate a few of them.

3. Buffalo Bills

Parts of the rating system wanted to rank the Bills No. 1. Their sack rate was incredibly high, only the Panthers caused more blown blocks that led to sacks, they shut down opponent's tight ends and running backs in the passing game, and they produced three Pro Bowlers (Kyle Williams, Marcell Dareus, Kiko Alonso) last year. Add some bonus points for new linebacker Brandon Spikes, and there are plenty of reasons to argue that this is the NFL's best front seven.

But there is a "continuity bonus" built into the system to boost teams with long-tenured coaching staffs, and the Bills scored a big goose-egg with their switch from a Mike Pettine multiple scheme to Jim Schwartz's radio WIDE-99.9, with the most predictable playlist on the dial. The Bills run defense is middle-of-the-pack, and there is a slim-but-frightening chance that Dareus will drag race off a cliff Rebel Without a Cause style, so moving them down a few slots seemed prudent. Still, based on sack production, personnel and potential, this is an outstanding front seven. Which is why I do not feel that uncomfortable ranking them ahead of …

4. San Francisco 49ers

This is the second unit ranking in a row for which the 49ers came out lower than I expected. A lot of midweek time and energy was spent determining why.

The 49ers finished fifth in the NFL in yards per game last season, fourth in rushing yards allowed, 18th in sacks and tied with the Bills and Cardinals for sixth in takeaways. The overall numbers are great, of course, but not legendary: it's not like the 49ers finished first (or second to the Seahawks) in every category. The ranking system uses no raw totals, but it is important to verify that the raw values underneath all of the high-tech metrics do not suggest that the 49ers deserve full-on 1985 Bears treatment.

The 49ers sack rate is extremely low: opponents threw 585 passes against them, yet the team registered just 38 sacks. The system compensates by giving the 49ers credit for shutting down tight ends and running backs in the passing game, the same credit that the Rams and Bills earned. The 49ers don't get any real boost from their run defense. The most special thing about the 49ers run defense is that it never, ever gives up a long gain: the longest run against them in the last three seasons was 35 yards. That feat, however, belongs partially to the secondary and will figure into next week's rankings.

Gosh, talking about a "system" sure is boring. The 49ers get credit for their Pro Bowlers and max points for system continuity, yet they barely cracked the top five. When you look at the talent above the 49ers, you can see that there is nothing ridiculous up there: those are teams with nasty pass rushes, stout run defenses and talent everywhere.

At the same time, the 49ers may be distorting their own statistics with their overall greatness. It was easy to see how good the Bills and Rams were at rushing the passer because they were bad at everything else: their key to winning was to maximize their true strength, and it showed up in the stat sheets. The 49ers are good at so many things that their success gets smeared all over the statistics. They win the field position battle every year (though the Chiefs nipped them this year), which cuts down on their total defensive plays, which cuts down on the number of devilish things they can do to an opponent. Their offense plays at a slow tempo (30th in the NFL), and they play with a lead nearly constantly. If their total 2013 time of possession were condensed into a per-game figure, the 49ers would have the lead for 38:47 and trail for a league low ten minutes and one second. Such extreme splits lead to a lot of time handing off for three-yard gains and watching opponents throw unproductive six-yard fourth-quarter passes. The system adjusts for such things, but not perfectly.

Oh well, if the 49ers keep ranking fifth or sixth in every category, that will send the message clearly enough. Some teams are better at this thing or that thing, but only one team can claim to be better at as many things.

Speaking of which, where are the Seahawks?

5. Kansas City Chiefs

The most interesting thing about the Chiefs' front seven is that it is a front five or six. Bob Sutton used nickel or dime personnel on over 66% of defensive plays last season, a high percentage even by today's "all nickel, all the time" standards. The Chiefs used just one or two defensive lineman on almost exactly half of all defensive plays. They essentially used a 2-4-5 or 2-3-6 base defense, which is a reminder of just how silly the 3-4/4-3 distinction has become.

If you consider the Chiefs' front seven a front six, you have to be particularly impressed that two-thirds of them reached the Pro Bowl: Dontari Poe, Tamba Hali, Justin Houston and Derrick Johnson. Tyson Jackson is gone, but Dee Ford has arrived, and it is easy to stay deep on the defensive line when you only use linemen one or two at a time.

You would think that all the nickel personnel would wreak havoc on the Chiefs run defense, but they finished in the middle of the pack in most metrics. In Power Situations (goal-to-go, third-and-short) they held opponents to a 56 percent conversion rate, seventh best in the NFL. So when it's time for Mike DeVito and Allen Bailey to take the field and give the Chiefs a big, conventional front, they get the job done. But pass rush and disruption are the name of the game for this defense, and while Sutton and the defensive backs contribute to the cause, this is one nasty defensive front.

Worth Mentioning

Top Ten: Seattle Seahawks. The free agent losses of Red Bryant, Chris Clemons and Clinton McDonald nudged the Seahawks out of the top five. No one loss is critical, but the three players combined to contribute a lot of productive plays in 2013: 11.5 sacks, 28 quarterback hits and Bryant's presence as a run stuffer cannot be shrugged off, even by a deep defense. There are also all manner of injuries among the linebacker corps to deal with: Bruce Irvin underwent offseason hip surgery, and while he plans to be ready for camp, it's one more example of the Seahawks' depth getting challenged.

That said, most of the gang is back, and the Seahawks suffer from the same syndrome that keeps the Niners from looking statistically awesome: opponents are sometimes too beaten down to even get sacked. This is still a great front seven, though it is still the third-best front seven in the NFC West, which illustrates what crazy times we live in.

Top Ten: New York Jets. Mo Wilkerson is the best unheralded defender in the NFL right now. He recorded 10.5 sacks, and his 45 total plays against the run held opponents to 1.6 yards per rush. Run defense is the name of the game for Rex Ryan's defense: Sheldon Richardson is good against the pass but great against the run (and has All Pro upside), Quinton Coples has developed into more of a run disruptor than a pass rusher and veteran Calvin Pace is an effective all-purpose system fit.

And then there is Damon "Big Snacks" Harrison, the nose defender who made 36 solo tackles without having a single tackle broken. The average play by Big Snacks took place 1.8 yards downfield, another example of a lineman wolfing down ball carriers so the linebacker do not have to do as much. When called upon, however, both David Harris and Demario Davis can deliver. We all know the many things Rex Ryan is bad at, so it is important to remember what he is good at: mixing and matching cocky rookies, aging specialists and guys named Big Snacks to create a stout, dangerous front seven.

On the Rise: Oakland Raiders. Adding Justin Tuck, Antonio Smith, LaMarr Woodley and Khalil Mack obviously upgrades the Raiders front seven. Tuck and Smith are over 30, Woodley blows out the candles in November, but the three veterans still have a little left. Mack, of course, is an outstanding all-purpose linebacker prospect.

It is important to note that these are 2014 rankings, not "future" rankings or "did the team do the right thing" rankings. The Raiders have assembled an Expendables-style front seven, but by next year most of its members will be expended. The team should enjoy the sacks, make Mack the best Mack he can become and hope it is enough to slingshot the rest of the organization into long-term competitiveness.

On the Rise: Atlanta Falcons. Tackling is a pretty fundamental component of defending, and the Falcons were lousy at it last year: opponents broke 83 tackles against the Falcons last season, fourth worst in the NFL. Defensive backs did much of the damage, but defensive tackle Jonathan Babineaux suffered nine broken tackles, the highest figure in the league for a defensive lineman, and there were other culprits scattered among the many rookies pressed into action last year.

Tyson Jackson, Paul Soliai and Ra'Shede Hageman represent a significant upgrade on the Falcons defensive line. None of the newcomers is a true pass rusher, but Kroy Biermann returns from injury to give the Falcons an all-purpose defensive end, while Sean Weatherspoon is expected back from a knee injury for the start of training camp. Weatherspoon was one of the sloppy tacklers of 2013, but the injury and inexperience around him played a role. A more hybridized scheme will also make best use of Biermann, give Osi Umenyiora a more specialized pass-rushing role and breathe some unpredictability into a defense that allowed 2,173 rushing yards while providing just 32 sacks last season.

From the Ashes: Chicago Bears. The Bears front seven was as bad as a front seven could be last year. It was not unusual for opponents to rush for over 175 yards and average six to nine yards per carry against the Bears in the second half of the season, when several key defenders were hurt and ends were playing defensive tackle so linebackers could play end. But the team took drastic counter-measures in the offseason, signing Lamarr Houston and Jared Allen while drafting Will Sutton and Ego Ferguson. There were some departures, including Henry Melton, but important pieces like Lance Briggs and Stephen Paea are healthy again, and the team doubled-down on veteran backups like Willie Young and Jordan Senn to ensure that they would break camp with seven defenders playing their proper positions.

The Bears would have ranked last without the upgrades, and needed just about every new face to squeak out of the bottom five. It is a shame the Bears did not face the Dolphins late last year. It would have been fascinating to watch two lines engage each other after the snap and get thrown 50 yards backward like Super Smash Brothers characters.

The Five Worst Front Sevens

28. Miami Dolphins

Olivier Vernon and Cameron Wake led a fine pass rush, but the Dolphins run defense allowed 1,998 yards despite a schedule full of average-to-terrible rushing opponents. Tight ends and running backs were frequently open in the passing game, as high-priced linebacker acquisitions Philip Wheeler and Dannell Ellerbe turned out to be ordinary defenders who just got paid a lot. As for Wake, he had eight tackles broken last season, the second-highest total in the league for a lineman; that does not make him a bad player, but it shows how even the Dolphins' best defenders have holes in their game. Finally, Paul Soliai is gone.

The Dolphins front seven is not terrible at any one position but is mediocre at about five, aging in critical places (Wake and Randy Starks are climbing down from Mount Thirty) and paper thin at linebacker. Their terrible offensive line made their defense look worse, but there are not many truly terrible defensive front sevens in the NFL, and the Dolphins graded out near the bottom of a pack of humdrum ones.

29. New York Giants

Losing Linval Joseph and Justin Tuck is going to hurt. Joseph was a mountainous presence inside, and while Tuck's competitive fire was starting to look like the barbecue pit after a long weekend, he could still ramp it up and dominate in short stretches. Youngsters Johnathan Hankins and Damontre Moore hope to step up, and Robert Ayers provides some depth as a rotation defender, but that is not a fair exchange, at least this year. Jason Pierre-Paul is either a Comeback Player of the Year candidate or vaporware.

The Giants line has gotten younger, but the linebackers have gotten older. The plucky late-round and free agent rookies of the 2011 Super Bowl run are still here -- Spencer Paysinger, Mark Herzlich, Jacquian Williams -- and they still would look much better as a special teams brigade than as regular contributors (though Paysinger has become a decent run defender). Jon Beason is back after his 2013 rebirth, while Jameel McClain arrives to test the theory that if your idea to improve your defense involves someone from the 2012 Ravens, you need a much better idea.

The Giants defense recorded just 33 sacks last year, 14 of them from linemen who are now gone. Most of the team's rebuilding resources went to the offense. Maybe Hankins and Moore will pay dividends in a year or two, but they will need additional reinforcements, particularly at linebacker.

30. Cleveland Browns

The curse of the 2012 Ravens strikes again! Paul Kruger was a pretty good player on a per-play basis but a lousy one on a per-dollar basis. The Browns invested so heavily in outside rushers last year (Kruger, Desmond Bryant, rookie Barkevious Mingo) that they practically cancelled each other out: the Browns managed just 40 sacks as former coordinator Ray Horton mixed-and-matched similar players into similar roles. Meanwhile, opponents converted 79 percent of short-yardage rushes against the Browns (worst figure in the NFL) and the team finished second-to-last in the league in stopping both running backs and tight ends in the passing game. Perhaps they needed fewer edge rushers tripping over each other and a few more conventional linemen and coverage linebackers.

Kruger and the others are talented, as is Phil Taylor at nose tackle, and Karlos Dansby replaces D'Qwell Jackson in a nearly one-to-one swap of veteran inside linebackers. Perhaps rearranging everyone can make a difference, and front seven feng shui is one of Mike Pettine's specialties. Of course, Horton was pretty good at that too, but sometimes you just have too many end tables and not enough chairs.

31. San Diego Chargers.

Name as many of them as you can. Thought so.

Okay, so you named Manti Te'o, Dwight Freeney and Jarret Johnson. That's two outside linebackers who will be a combined 67 years old when the season starts, plus a "controversy" guy coming off a passable rookie season. There is other talent sprinkled here and there, like end Corey Liuget and Melvin Ingram, a once-exciting prospect who most of 2013 to injuries. But there are no high-level difference makers, and few significant newcomers. A team that registered just 34 sacks last season cannot rejoice in just holding serve.

Run defense was a bigger issue than pass rush for the Chargers last year. Opponents converted 73 percent of "power" situations (26th in the NFL) and the Chargers stuffed just 16 percent of opposing rushers (27th). The defense allowed few long runs, which means that opponents averaged 4.6 yards per attempt by gouging out consistent four-to-five yard rushes. Nose tackle Cam Thomas (now in Pittsburgh) will be replaced by Sean Lissemore, a former Cowboys prospect coming off a shoulder injury. If that's an upgrade, it's a pretty minor one.

32. Dallas Cowboys

The Cowboys lost DeMarcus Ware, Jason Hatcher and (in the saddest, most ridiculous minicamp story of the year) Sean Lee from a defense that allowed 2,056 rushing yards and recorded just 36 sacks last year. Henry Melton arrives as a younger, more system-suited replacement for Hatcher, but everything else is a shambles. Bruce Carter, Justin Durant and DeVonte Holloman form the most anonymous linebacker corps in the league, and only Carter has any significant starting experience. Anthony Spencer may start the season on the PUP list as he battles back from microfracture surgery on his knee. And of course, the Cowboys are so cap-stressed that they wouldn't be able to sign a veteran reinforcement, even if one becomes available this late in the offseason.

The wisest thing the Cowboys could do is insert rookies Demarcus Lawrence and Anthony Hitchens into the rotation quickly and let them learn on the job. The Cowboys did not get into this predicament by doing the wise thing. But they are so thin and talent-poor that they may not have a choice.

Next Week:

Will anyone challenge the Seahawks for the top spot in the secondary rankings? No. But check back to see who finishes second, and who grades out the worst. Also, don't forget to order ten to 15 copies of my new book. A Good Walkthrough Spoiled: the Best of Mike Tanier at Football Outsiders was briefly outselling Tim Tebow's book last week, and it has a five-star Amazon rating thanks to one of you giving me a great review. Let's keep the momentum flowing!