The NFL's most improved position groups since the end of last season

Which teams did the best job of addressing their worst units? It doesn't always come down to the big-money signings.

Individual big-name signings get all the headlines when NFL teams reload their rosters every off-season, but the smart front offices are ultimately rewarded for building the deepest, most talented position groups in a sport built on interdependent skill sets. With that in mind, here are 10 of the most improved position groups ahead of the 2015 season.

Jets secondary: The pass defense that had been so formidable for so many years of Rex Ryan's tenure was anything but in his final year as Jets coach. This was more about a series of bungled moves by ex-general manager John Idzik, but Rex had little to work with in his secondary in 2014. A unit once led by Darrelle Revis and Antonio Cromartie patrolling the defensive backfield as well as any duo in the NFL, with a group of corner/slot/safety hybrid guys filling in the blanks, had Darrin Walls as its primary cornerback last season.

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After Ryan was replaced by former Cardinals defensive coordinator Todd Bowles, new GM Mike Maccagnan went after a new secondary in a very old-school way. He brought back Revis and Cromartie on lucrative multi-year deals and signed ex-Browns cornerback Buster Skrine to play the slot. At safety, veteran Marcus Gilchrist was brought in to guide 2014 first-rounder Calvin Pryor. As long as Revis and Cromartie still have their fastballs, it's tough to think of any position group that improved more this off-season.

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Dolphins defensive line: The six-year, $114 million contract given to Ndamukong Suh was free agency's biggest splash, but the Dolphins went even further to upgrade a front four that fell apart down the stretch and cost them a legitimate shot at a playoff berth. Miami also brought in Suh's Lions teammate C.J. Mosley, an underrated veteran who played pretty spectacularly when filling in for the injured Nick Fairley in 2014. Putting Suh and elite pass rusher Cameron Wake on one side of the defense should open up a lot of single-team opportunities for Olivier Vernon on the other end of the line.

Former Texans nose tackle Earl Mitchell was a great addition a year ago, but don't sleep on rookie tackle Jordan Phillips, who was perhaps the most athletic player at his position in this year's draft. This unit should make things very, very difficult for opposing offensive lines in 2015 and beyond.

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Cowboys defensive line: In 2014, the Dallas defense surprised thanks to Rod Marinelli's coaching and the time-of-possession advantages offered by a dominant running game. The secondary was average at best, a problem compounded by a front four that struggled to bring consistent pressure. Jeremy Mincey led the team with six sacks, and although he was able to add seven quarterback hits and 37 quarterback hurries, more firepower up front was required.

The Cowboys are banking on two controversial pickups to upgrade their pass rush: former Panthers end Greg Hardy and second-round draft pick Randy Gregory. Hardy's off-field issues are well-documented, but he's one of the league's more dominant 4–3 ends when he's active. Gregory was an athletic freak for the Cornhuskers, zipping around the edge at around 230 pounds. He'll have to bulk up a bit and overcome the off-field concerns that led to his draft-night slide, but he's looked spectacular in the preseason. Hardy will miss the first four games, but watch out once this group all gets on the field at the same time.

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​Browns defensive line: Despite the Browns' horrible quarterback situation, they may have reached the .500 mark last season if not for a run defense that was porous at best and ridiculous at worst. Only the Saints ranked lower in Football Outsiders' opponent-adjusted run defense metrics, and that simply won't fly in the AFC North. Step one in turning things around was the selection of Washington defensive tackle Danny Shelton with the 12th pick in the 2015 draft. A 6'2", 329-pound monster in the middle, Shelton is a perfect fit for head coach Mike Pettine's defense because he can manhandle opposing guards and centers in run and pass situations, and he can do it out of one-gap and two-gap sets.

The Browns also picked up Randy Starks from the Dolphins as a veteran situational pass rusher, and holdover Desmond Bryant will help, as well, but the addition of Shelton alone would redefine this Cleveland front. He calls to mind Vince Wilfork at his peak with his unearthly combination of power and agility. If outside linebackers Paul Kruger and Barkevious Mingo can keep the pressure up, Cleveland might have the best defense in the division.

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Colts receivers: The Colts have finished 11–5 for three straight years, pretty impressive consistency for a team with just three marquee talents: quarterback Andrew Luck, receiver T.Y. Hilton and cornerback Vontae Davis. Luck hasn't really had a big, reliable possession receiver throughout his time in Indianapolis, which makes the acquisition of Andre Johnson so intriguing. Luck is a full-field-vision player with outstanding mobility and the ability to make any throw, but between the lack of intermediate help and almost no running game, it was up to him too often to define and extend the team's offensive drives.

No longer. Johnson, who caught 85 passes for 936 yards and three touchdowns for a Texans team with no discernible quarterback in 2014, is understandably happy about the upgrade at that position in his new home. You can also expect bigger things from second-year receiver Donte Moncrief, and the selection of Miami speedster Phillip Dorsett gives Luck another quick vertical receiver to pair with Hilton. Luck threw for a league-leading 40 touchdowns in a limited system last season. The sky could be the limit now.

Falcons defensive line: When the Falcons tabbed former Seahawks defensive coordinator Dan Quinn as their head coach, you knew things were going to change along the defensive front. Under general manager Thomas Dimitroff, the franchise has whiffed on potential pass rusher after potential pass rusher, but Quinn is one of the more creative minds in the business when it comes to personnel placement in 4–3 fronts. The overhaul started with the selection of Clemson pass rusher Vic Beasley with the No. 8 pick. Beasley needs to get stronger to deal with NFL offensive tackles, but he absolutely flies off the snap and could be an optimal LEO end in Quinn's system.

Veterans Jordan Babineaux and Paul Soliai are projected to man the middle, with Adrian Clayborn as the strong-side end, but you never know how Quinn's going to line people up. Clayborn could play tackle at times with Soliai as a super-sized end. Watch out for fifth-round pick Grady Jarrett; the Clemson product could be the next great undersized penetration tackle in the mold of Geno Atkins and Aaron Donald.

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Seahawks pass catchers: The Pete Carroll era in Seattle has been defined by fundamentals, a tremendous running game and the NFL's best defense. The team's receivers have never merited top billing, although Doug Baldwin has always been an underrated player. The Seahawks tried to add explosiveness by trading a first-round pick to the Vikings for Percy Harvin in 2013, but Harvin struggled to follow up on a few flashes of brilliance.

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This spring, general manager John Schneider elected to again deal from his stock of draft picks, sending a first-rounder and center Max Unger to the Saints for tight end Jimmy Graham, unquestionably the most gifted receiver this franchise has seen since Steve Largent. Graham isn't much of a blocker, but he doesn't have to be. He creates nightmare matchups all over the field and especially in the red zone, a problem area for Seattle's passing game in the last few seasons.

In the draft, Seattle moved up to take Kansas State receiver Tyler Lockett with the 69th pick, and the prolific speedster has already proven to be a dynamite addition in the return game with two preseason touchdowns. He'll provide additional value as a slot receiver who can push safeties to their limits. For the first time in years, the Seahawks may have a balanced offense—as long as the offensive line can hold up just enough for Russell Wilson to survive anything more than a three-step drop.

Titans receivers: No. 2 pick Marcus Mariota should help this dismal offense quite a bit, but Mariota is going to need targets, and the Tennessee front office has done a decent job of upgrading the position. The second-round selection of Dorial Green-Beckham could pay huge dividends if the super-talented receiver keeps his off-field actions in line. Harry Douglas and Hakeem Nicks are unspectacular but professional additions who will at least give Mariota targets to lean on in short-yardage situations. No. 1 receiver Kendall Wright had his ups and downs in 2014, but he's already clicked with Mariota in the preseason, and that chemistry should continue to build.

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​Eagles secondary: Things couldn't have been much worse than they were last year. Cornerbacks Bradley Fletcher and Cary Williams were encouraged to leave the premises as soon as possible after the season, and between Fletcher's spectacular coverage lapses and Williams's deadly combination of inconsistency and attitude, that was the right move. Signing ex-Seahawks cornerback Byron Maxwell to a six-year, $63 million contract with $25 million guaranteed was a bit of an overpay, but at least defensive coordinator Billy Davis finally has one pass defender who can trail No. 1 receivers and won't fall down in bail coverage.

Second-round pick Eric Rowe is projected to be the starter opposite Maxwell, and Rowe can play safety in a pinch as well. Outside of Malcolm Jenkins, safety is a question mark, but the team has been experimenting with former Seahawks slot corner Walter Thurmond in that role, and Thurmond has performed admirably. All signs point to improvement for a team that now looks like the favorites in the NFC East.

Lions running backs: Detroit added a new Thunder and Lightning duo of rookies to a unit that was roughly league-average in 2014. Second-round pick Ameer Abdullah reminds some of LeSean McCoy with his combination of straight-line speed and short-area agility, and undrafted free agent Zach Zenner has been a preseason sensation—the South Dakota State product currently leads all rushers this month with 162 yards on 25 carries. Whether Zenner can carry that forward into the regular season remains to be seen, but in Abdullah, Detroit has a legitimate top-tier back for the first time in the Matthew Stafford era. And if this team can shore up the consistency in the run game with their aerial attack and excellent defense, they could change the complexion of the NFC.