Welcome back to the Rankings File, an ongoing spring and summer season rating the best and worst units in the NFL. This week, we cover the defensive backs.

No fake suspense this week. No reason to scroll down. The Seahawks ranked first. Go ahead and argue otherwise, once you are finished posting to your Flat Earth message board. But don't click away just yet: There is plenty of intrigue for spots two through five and in the bottom five. There's also a serious question to explore as we rank these secondaries: Just how do you go about ranking a secondary?

You cannot use passing yards, because great defenses often go into prevent mode in fourth quarters, while bad defenses face coasting offenses late in games. That was not as much of a problem this year as it has been in years past: The Seahawks led the NFL by allowing just 273.6 yards per game, because they are that good. But passing yards allowed are a notoriously counterintuitive stat.

Interceptions, meanwhile, are seven to 28 isolated events scattered across hundreds of pass plays. The top intercepting team is often the one that faced the most rookie quarterbacks; a tremendous secondary might finish in the middle of the interception pack as teams execute arch-conservative game plans whenever possible. Again, this was not a problem in 2013, when the Seahawks led the league with 28 interceptions, but it plagues analysis in most seasons.

Football Outsiders uses the DVOA metric to break down the success level of every passing play of the season, cutting through much of the distortion. They also break down success rates by wide receiver, and you will see some of that analysis in the ratings below. If a defense consistently shuts down Calvin Johnson and Dez Bryant while giving up big games to Kris Durham and Cole Beasley, we can hypothesize that their top cornerback was great but their second cornerback wasn't.

The key word is "hypothesize." Football Outsiders uses game charting to determine how many passes each cornerback allowed, broken up and so on. Here's a link to the top cornerbacks of 2013, and another to the worst. Other stat services use similar play-by-play analysis, usually tabulating similar results. Here's the problem: There is no way a tabulation of catches and yards can account for man or zone defense, safety help (or lack thereof) or -- and this is a huge one -- quality of pass rush. So a top cornerback isolated in man coverage against Julio Jones will have a hard time looking as good as a nickel corner covering Harry Douglas in an underneath zone with a safety behind him. And both will look far better if the quarterback is pressured consistently. That's why Football Outsiders does not accumulate all of its data into some scientific-looking individual rating for players. The data is part of an evaluation process, not an evaluative conclusion.

These rankings take all of that high-tech data, blend it with the Pro Bowl ballots and scouting reports on recent prospects, pour in a few quarts of film study, spike it with common sense and rim the glass with a grain of salt. The results should be pretty smooth drinking. If nothing else, the first sip is guaranteed to go down easily.

The Five Best Secondaries

1. Seattle Seahawks

That was easy. Here's a harder question: Where do the Seahawks rank among the greatest secondaries of all time? Too soon, you say? I disagree, and over at the Tailgater blog, I am ready to put them in the all-time Top Five.

2. Cincinnati Bengals

When we think about the Bengals defense, we generally think about the front seven. And yes, the line and linebackers made a contribution to this ranking; the same can be said of all defenses. But the Bengals finished third in the NFL at stopping No. 1 receivers, third against No. 2 receivers and sixth against Nos. 3-5 receivers. They did it with Geno Atkins hurt for much of the year, sapping some of their pass-rush capability. So the secondary was doing something right.

The Bengals have an odd mix of veterans and youngsters at cornerback and safety. Terence Newman is still finding a way to hold down a starting job at 35, Reggie Nelson and Adam Jones are both 30 (Pacman at 30: the lion in winter) and 31-year old Danieal Manning has arrived as a veteran option at safety. Across the generation gap are first-round pick Darqueze Dennard, third-year pros Dre Kirkpatrick and Geogre Iloka and second-year project Shawn Williams. Leon Hall probably decides which radio station gets played in the locker room.

Mike Zimmer was capable of getting the best out of both the veterans and kids last year. Hall played at a high level before getting hurt, with Kirkpatrick coming into his own as a replacement, contributing to that high "slot receiver" ranking. Jones still has 90 percent of the off-the-charts talent of his younger years but has cut down on the silliness by about 75 percent. The Bengals played lots of man coverage last year, with Nelson sometimes blitzing or covering a tight end/slot guy and Iloka roving, so Bengals corners often faced difficult assignments. They kept plays in front of them well, tackled flat and screen receivers for minimal gains, shut down first reads and of course helped the defense intercept 20 passes.

When you watch Bengals game tape (I watched an extra allotment this week, because this ranking looked fishy to me), it's enlightening how often quarterbacks like Aaron Rodgers and Philip Rivers pump-fake, check down and leave the pocket to buy time, a sign that the Bengals secondary has clamped down on the original route combination.

Dennard's arrival provides an additional boost. He is a natural cover corner who should step in as Newman finally runs out of Just for Men. Williams barely played last year but appeared to be coming around late in 2013 training camp. There is tons of depth here, and new coordinator Paul Guenther won't be making any major changes. The Bengals secondary does not pop out at you, but it doesn't let you complete many passes, either.

3. Arizona Cardinals

When a team has one great cornerback and one less-than-great cornerback, you can usually see it in the raw statistics. The great cornerback will look like he was just standing around all year: few tackles, few interceptions, some passes defensed. The not-so-great guy will be the stat-sheet superstar, with gobs of tackles and a high total of passes defensed.

You know what's going on, of course: Teams are avoiding the great corner and picking on the other guy, who winds up with some interceptions and passes defensed because he is in the crosshairs so often, plus lots of tackles after he allowed a reception. Such was the situation with Patrick Peterson, with 40 solo tackles, three interceptions and 13 passes defensed, vs. Jerraud Powers, with 60-1-17.

Peterson, an All-Pro and the one guy in the NFL who really can nitpick Richard Sherman's game, made the Cardinals the top-rated team in the NFL at shutting down opponents' No. 1 receivers. Powers was not terrible, but he was targeted 104 times to Peterson's 85, allowing eight yards per catch to Peterson's 6.4.

The best complementary cornerback to a player of Peterson's skills is a ballhawk who can turn tons of targets into turnovers. New arrival Antonio Cromartie has made a career out of just that. Miscast as a top cover corner last year, Cromartie previously thrived when opponents had to throw the kitchen sink at their second-best receivers to avoid Darrelle Revis. As a No. 1 cornerback last year, Cromartie's errors overwhelmed his interceptions. Back in his natural role, Cromartie will be a headache for opponents, with Powers sticking around as the nickel corner.

Then there is Tyrann Mathieu, who crammed 16 games worth of "OMG this kid can fly" into 13 games before getting hurt. Mathieu's advanced stats look great, but advanced stats don't tell his story. Todd Bowles uses him as something between a free safety, nickel corner, roving linebacker and Snake Eyes from G.I. Joe. Mathieu typically mixed one or two out-of-position or double-moved rookie blunders per game with plays where he looked like he was tapping his feet and waiting for the receiver to make a move so he could either undercut the route or deliver a hit. Mathieu is not expected back in the lineup until Oct. 1. If he were healthy today, the Cardinals would rank ahead of the Bengals.

Mathieu has tremendous upside, and rookie Deone Bucannon can run and crunch. Both can do whatever strikes Bowles' fancy on most plays, because Peterson can take care of himself, and when Cromartie decides to bet the mortgage on a guess no safety can protect him. This is a young, gifted, nasty group whose skills feed off each other and play into the hands of a daring defensive coordinator.

4. New York Giants

The Giants entered the offseason with a great safety (Antrel Rolle), an outstanding nickel defender (Trumaine McBride) and lots of questions. They then added Dominique Rodgers-Cromartie, Walter Thurmond and Quentin Demps to fill in the ample cracks. For the Giants, that's roughly six years' worth of free-agent acquisitions in a month, and the results should be immediate.

DRC and Thurmond both arrive with some questions, but Rodgers-Cromartie's ability to gamble-and-bait is a major step up from Terrell Thomas' attempt to recapture his pre-multiple-ACL-tear form, while Thurmond was a valuable role player in Seattle before injuries and suspensions. Prince Amukamara allows too many short receptions but few deep ones, and he is still developing after an early career filled with injuries. Amukamara and DRC should complement each other well, while McBride was a 2013 revelation after years of practice squad and bench bouncing.

Rolle, meanwhile, leads a safety corps that excelled at shutting down long running plays last year, and Demps is a natural free safety who can allow Rolle to prowl close to the line of scrimmage. The Giants secondary stats looked great last year. Part of that was Rolle and McBride (and Amukamara and Thomas' ability to keep things manageable), part of it was coordinator Perry Fewell, who adjusts his system to keep players out of bad positions. But part of it was a terrible offense that allowed opponents to play conservatively to beat the Giants. Fewell, Rolle and some others are still here, but with all the reinforcements, they won't need the offense to look bad to make the secondary look better.

5. Cleveland Browns

Remember how Patrick Peterson made Jerraud Powers' raw numbers look good in the Cardinals comment? Well, Joe Haden was targeted 88 times last year, allowing 6.1 yards per attempt en route to 43 solo tackles, four picks and 20 passes defensed. Buster Skrine was targeted 105 times, allowing 5.9 yards per attempt (surprise!) with 54-1-17. Skrine also allowed 13 broken tackles, an incredibly high total for a cornerback, so his impressive yards-per-attempt comes with a big lump of skepticism. As is the case with Powers, Skrine will look a heck of a lot better getting matched up against No. 3 receivers than playing every snap.

Rookie Justin Gilbert should take over as Haden's partner at cornerback right away, and Mike Pettine brought in slot specialist Isaiah Trufant to battle Skrine for the right to cover those 5-foot-9 jitterbugs. Leon McFadden, famous for committing "pass interference" in the end zone against the Patriots last year, is also back, and rookie Pierre Desir adds even more depth.

At safety, Donte Whitner is a downgrade from T.J. Ward but still a guy who makes the news crawl when he gives himself a silly name, while Tashaun Gipson has grown into a fine centerfielder, intercepting five passes last season while breaking up seven others (a few of which should have been intercepted). Start with a Pro Bowl corner, add a battle-tested safety and a top-shelf rookie, add a bunch of young defenders who did pretty well under difficult circumstances last year, and you have a top-five secondary.

Worth Mentioning

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Jimmy Smith broke out last year to help the Ravens shut down No. 1 receivers. (USA TODAY Sports)

Top 10: Baltimore Ravens. Jimmy Smith was excellent last year: 6.3 yards allowed per pass (10th in NFL), a 59 percent success rate at stopping receivers (12th), a massive role in making the Ravens the second-best team in the NFL at stopping No. 1 receivers. It's a reminder that you really, really need three years to evaluate a Ravens draft, because Smith spent two years looking like the guy who would never figure things out. Ladarius Webb was his usual reliable self (22 passes defensed), and Matt Elam had a pretty good rookie year. The Ravens might have cracked the top five if they hadn't lost Corey Graham to the Bills and James Ihedigbo to the Lions, leaving them thin at safety and in nickel situations. Then again, the team drafted Asa Jackson in the fifth round in 2012. He may need just a few more hours in the Harbaugh-Newsome Slow Cooker.

Top 10: San Francisco 49ers. As a regular feature in the Rankings File series, the 49ers lurk somewhere near the bottom of the top 10, making the whole series look like an extended 49ers snub. As mentioned last week, this will probably keep happening, because the quality of one 49ers unit tends to bleed into all the other units, making none of them look spectacular but all of them look great, while some of the things the 49ers excel at (depth, situational football), are tricky to analyze on a unit-by-unit basis.

At least the 49ers have lost Tarell Brown, Donte Whitner and Carlos Rogers in the secondary, making it easier to explain why they have slipped. Then again, Eric Reid is coming off an excellent rookie season, Jimmie Ward was one of my favorite prospects in the 2014 draft class and Antoine Bethea arrived to take the sting out of Whitner's departure. Potential starting cornerbacks like Tramaine Brock and Chris Culliver can count on support from both the safeties in zone coverage and the pass rush, plus a stingy run defense, great field-position advantages and on and on.

Like the Bengals, the 49ers might have ended up with a front seven ranked too low and a secondary ranked too high, because it is simply impossible to separate defensive components precisely. Or perhaps our perceptions are wrong and the rankings are right. Either way, this looks like an exceptional safety corps with some so-so cornerbacks flanking it.

On the Rise: New Orleans Saints. The Saints pass defense stats looked great last season, but their front seven and scheme had a lot to do with that. The front seven will still be very good this year, but the secondary won't need as many favors.

Kenny Vaccaro and Jairus Byrd will form one of the best, most natural safety tandems in the NFL this year. Rob Ryan will send Vaccaro all over the formation looking for trouble while Byrd impersonates Torii Hunter circa 2003. Jabari Greer is gone, but Keenan Lewis proved to be a fine Ryan system fit last year, and rookie Stanley Jean-Baptiste will be a useful puzzle piece when the Saints match up against big receivers or speedy tight ends.

Also, future Hall of Famer Champ Bailey is on the roster. Bailey cannot lock down on Julio Jones anymore, but what about Bailey in underneath coverage with Byrd up top while Vaccaro blitzes? Ryan probably wakes up at dawn because he is so excited to scribble down new coverage ideas.

Hard to Classify: Kansas City Chiefs. The Chiefs released Brandon Flowers this week. Flowers got hammered by the Football Outsiders metrics, allowing 9.3 yards per pass attempt (adjusted, with long touchdowns prorated so they do not skew the results) and posting a low success rate at stopping receptions. Marcus Cooper's numbers were similar to Flowers', but Cooper was a late-arriving rookie thrust into a regular role, while Flowers was a veteran. Two regular cornerbacks with terrible charting results would normally be a sign of a bad secondary, yet the Chiefs ranked in the top half of the NFL according to my system, and the team produced two Pro Bowlers: Eric Berry and Flowers.

The Chiefs' defensive passing statistics were very good last year. They allowed 4,271 yards but just a 56.4 percent completion rate and 21 interceptions, meaning that opponents were throwing a lot but paying for it. Then again, they faced a legendary string of third-string quarterbacks in midseason. No coordinator in the NFL uses his safeties and corners the way Bob Sutton uses them: Chiefs defensive backs blitz from multiple angles and serve as de factor linebackers in 2-3-6 personnel groupings constantly. So comparing a Sutton secondary to, say, a Cover-2 based secondary results in all sorts of distortions. The Chiefs are great illustrators of why it is useless to evaluate defensive backs by adding up the plays they made or missed.

With Flowers and Quintin Demps gone, the Chiefs had no chance of cracking the top five. With Berry, Sean Smith, Cooper and some prospects in the pipeline, they are safe from the bottom five. Sutton will keep using the Chiefs secondary in strange ways, but he won't have Jeff Tuel to kick around this year, so we'll get a better sense of where the quality ends and distortions begin.

From the Ashes: Oakland Raiders. The Raiders secondary has been a disaster for years, though it has been easy to overlook because the team had so many other problems. Last year, they were down to Tyvon Branch and a bunch of old guys on a reunion tour, with Charles Woodson looking like Pete Townshend trying to play Quadrophenia one more time without going deaf or keeling over.

Woodson is back -- he may actually be assistant general manager at this point, keeping himself on payroll because he can -- but the rest of Branch's supporting cast got an upgrade. Which is good, because as a strong safety, Branch is supposed to be part of a supporting cast. (Marcel Reece feels his pain on offense.) D.J. Hayden, last year's first-round pick, is healthy and ready to make a contribution. Yes, that's a statement frequently made about Hayden in late spring but rarely made in mid-autumn, but it's a start. Tarell Brown and Carlos Rogers cross the bay from San Francisco to provide credibility at cornerback behind Hayden. Both are further examples of veteran spackling on a roster that requires major rebuilding -- see the entire defensive line -- but Brown has a few good years left, Rogers at least one and Hayden now has a whole Hogwarts worth of mentors. The Raiders won't be moving safeties over to play cornerback or calling Lester Hayes out of retirement this year.

The Five Worst Secondaries

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The Vikings' mistake-prone secondary is in the middle of a rebuilding project. (USA TODAY Sports)

28. Minnesota Vikings

The Vikings made multiple improvements in the offseason to climb up from dead last. Captain Munnerlyn is an example of the type of cornerback who grows from plucky special-teamer to nickel guy to someone who can have a Pro Bowl-caliber season on a team with a nasty pass rush. He's miscast as the top cornerback on a rebuilding team, which is why the Vikings did not crawl out of the bottom five by signing him.

Xavier Rhodes takes over as the other Vikings cornerback after a typical rookie-like rookie season. Munnerlyn and Rhodes replace two of the league's worst cornerbacks: Chris Cook and Josh Robinson, a pair of prospects who never developed and ranked near the bottom of the league in just about any stat you can use to measure cornerbacks. Robinson is still lurking as a nickel corner.

Harrison Smith's return gives the Vikings an excellent all-purpose safety, but Jamarca Sanford is a talented mistake machine at the other safety slot. There are few truly awful secondaries in the NFL, because teams make drastic upgrades when it becomes obvious that they cannot stop a forward pass. After giving up 4,869 yards and 37 touchdowns last season, the Vikings are still in the midst of their drastic upgrades.

29. San Diego Chargers

Despite the presence of Eric Weddle and the arrival of first-round pick Jason Verrett, the Chargers cannot escape the bottom five. Shareece Wright is the primary problem. Football Outsiders uses a Success Rate stat to determine just how often a cornerback prevented a meaningful completion (allowing an eight-yard catch on third-and-10 is considered a "success"). Wright's Success Rate was just 38 percent, fifth lowest in the NFL. Two of the guys below him are coming up in this roundup of the worst secondaries, while the others were just mentioned in the Vikings section. Wright is still a starter and theoretically the No. 1 Chargers cornerback until Verrett gets his feet wet.

Converted cornerback Marcus Gilchrist is a mistake-prone cleanup defender at safety next to Weddle. Nickel defender Richard Marshall will get pushed by Steve Williams, who is essentially a redshirt freshman after missing all of last year with a pectoral tear. These guys aren't likely to get much of a boost from the pass rush, and they have to face Peyton Manning twice per year, plus the NFC West powerhouses. The good news is that NFC West powerhouses don't test cornerbacks much after the first half, because they do not have to.

30. Jacksonville Jaguars

The Jaguars have adopted a "one catastrophe at a time" rebuilding program, and while they devoted some draft resources to the secondary last year, a more thorough overhaul is still at the bottom of their punch list. Last year's arrivals do have plenty of potential: 2013 second-round pick Jonathan Cyprien showed promise as a fly-around safety, and third-round pick Dwayne Gratz played well between ankle injuries, looking like the kind of physical bump-and-run guy Gus Bradley wants for his Florida Seahawks. Veteran Alan Ball also played well last year.

After two prospects and a reliable veteran, things get ugly fast. Will Blackman looks like a Bradley cornerback -- HE'S TALL -- but plays like a journeyman whom multiple teams gave up on. Josh Evans' average tackle occurred 12.4 yards down the field, which is a reflection of both his teammates and his role but also a sign that he is more of a fill-in than a prospect in Cyprien and Gratz's class. There are no impact rookies, because the Jaguars focused on their offensive skill positions in this draft.

We are about to look at another secondary full of second-year players. That team, like the Jaguars, could take a big leap forward in 2014. Until they start leaping, we have little choice but to rank them this low. The bust rate on young corners and safeties is high, and when a team counts on prospects in bunches, sometimes they put too much pressure on too many youngsters too soon.

31. Atlanta Falcons

The 2013 storyline: Asante Samuel was old and terrible; everyone else was a rookie. The 2014 storyline: Samuel is finally gone, and everyone is now a second-year player, but you have to do a lot of projecting to erase what happened in 2013.

Desmond Trufant came on strong late last year, and with a name like "Trufant" comes the expectation of a solid career. Robert Alford spent most of last season getting picked on, however, and nickel corner Robert McClain allowed 11.3 yards per pass attempt (adjusted), the third-worst rate in the NFL. (Antonio Cromartie, stuck in a bad fit, was first; Samuel was second.) Oft-injured Dwight Lowery arrives from Jacksonville to replace Thomas DeCoud, who only looked like a great tackler in recent years because he stood next to Samuel. Rookie Dezmen Southward adds safety depth, but if the Falcons secondary gets any younger their games will become a Disney XD series. William Moore is probably still good. If you can evaluate a safety wedged between Samuel, DeCoud and two rookies with precision, you are a better tape grinder than I am.

If Brandon Flowers returns Scott Pioli's calls and joins the Falcons, they at least move up to the Vikings level.

32. Detroit Lions

The loss of Chris Houston dropped the Lions from 31st to 32nd late in the writing process. Houston is an adequate starter, which sounds like an insult until you realize that most NFL starters are essentially just adequate starters. (If all of them are great, then greatness becomes merely adequate, because winning then requires superior greatness.) Anyway, the Lions were thin before releasing Houston for injury (plus cap) reasons, and they are too close to their credit card limit to sign a replacement.

Second-year cornerback Darius Slay generated some minicamp buzz. It wasn't the usual "everything is awesome" buzz -- minicamp news and The Lego Movie have much in common -- but "he has improved his footwork at the top of the receiver's route" buzz. Specificity is good when trying to decode offseason news. But the safeties are -- here's that word again -- adequate, Bill Bentley is now penciled in as a starter and depth consists mainly of late-round picks.

And then there is Rashean Mathis, once a very good cornerback for some very good Jaguars teams of yesteryear. There are some names on a depth chart that just scream "these guys don't have a handle on this position." Chris Williams is one. Mathis is another. If he is pressed into regular duty, the Lions' season will consist of nonstop 38-34 games, and the Lions are only going to be able to win a few of them.

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Next Week: The receiver corps do battle. Will the Broncos or Bengals come out on top, or is some dark horse jockeying to take the crown? In other news, my new book is now available in Kindle format! A Good Walkthrough Spoiled is essential summer reading: the only book that dares to taste-test Chad Ochocinco cereal, debate the greatness of John Riggins and tell the true story of the 1987 replacement games. It's like a 400-page midlife crisis, plus play diagrams, and with Norman Mailer long dead, it's the only game in town if that is what you are into.