NFL's best defenses: Who got better, worse, and who's next up

Despite the three months that remain until kickoff, a handful of NFL teams are vying to stay in the conversation among the league’s best defenses long before they play a single snap in 2018.

During the offseason, these teams took steps via pricey free-agent acquisitions, trades and the draft to make marked improvements to their defensive personnel; moves that aim to bolster the championship aspirations many of them already had.

Here’s a look at where things stand for the top five defenses from last year, from roster additions and subtractions to how much better or worse each got, as well as which other team might crack the top five by the season’s end.

Minnesota Vikings

2017 NFL rank: First (total defense)

Major additions: DT Sheldon Richardson, CB Mike Hughes

Major losses: DT Tom Johnson, NT Shamar Stephen, LB Emmanuel Lamur

2018 outlook: The Vikings already had one of the most talented defenses in the NFL before they signed Sheldon Richardson to a one-year deal in free agency. Adding Richardson to the league’s reigning top defense not only upgrades the 3-technique spot, it solidifies Minnesota as a Super Bowl contender. Richardson earned a top-10 pass-rushing grade from Pro Football Focus last season and should provide a serious push from the interior next to Linval Joseph. Between those two and edge rushers Everson Griffen, who is coming off a career sack year despite battling through plantar fasciitis, and Danielle Hunter, the Vikings will rival the likes of Philadelphia and Jacksonville as the best D-line in the NFL. Mike Zimmer’s stout defense finished first in yards (275.9) and points allowed (15.8) last season while holding quarterbacks to a 73.0 passer rating. The rich got richer in the draft when Minnesota focused a bulk of its efforts on adding depth pieces, from selecting cornerback Mike Hughes at No. 30 to drafting players to compete for a spot in the defensive line rotation, an element that was missing in 2017.

Zimmer hinted at wanting to experiment with four cornerbacks in some of Minnesota’s sub packages, and having a player like Hughes, along with three other first-rounders in the secondary alone (Harrison Smith, Xavier Rhodes and Trae Waynes) should allow the Vikings to utilize exotic looks often. That will be critical given the elite passers they’re set to face this season, from Aaron Rodgers to Tom Brady to Carson Wentz, Jared Goff, Jimmy Garoppolo and Russell Wilson. Minnesota could use some more depth at linebacker, and if the Vikings don’t sign a veteran free agent this summer, training camp will feature an important position battle to see who will fill that void, particularly at outside linebacker. Minnesota locked up Eric Kendricks to a long-term deal in April and could be looking to do the same with Anthony Barr next. The strength of this franchise has long been its defense. The moves the Vikings made this offseason reflect that, putting Minnesota in prime position to continue its run as the NFL's top defense. -- Courtney Cronin

Jacksonville Jaguars

2017 NFL rank: Second

Major additions: DT Taven Bryan, CB D.J. Hayden, S Ronnie Harrison

Major losses: CB Aaron Colvin, LB Paul Posluszny

2018 outlook: The Jaguars return 12 of their top 14 defensive players from last season, including six Pro Bowlers: DE Calais Campbell, DT Malik Jackson, DE Yannick Ngakoue, LB Telvin Smith, CB Jalen Ramsey, CB A.J. Bouye. Campbell and Ramsey also were first-team All-Pros. Colvin was the nickelback and the Jaguars signed Hayden to replace him. Myles Jack moves inside full-time to replace Posluszny, and second-year player Blair Brown takes over at strongside linebacker. Those are the only changes from a unit that ranked second in interceptions and sacks and first in pass defense. Ramsey and Bouye are arguably the best cornerback tandem in the NFL, and Bouye has come back with a chip on his shoulder because he felt he got slighted by not making the All-Pro team. The defense had some issues later in the season, giving up at least 24 points in five of the final nine games (including twice in the playoffs), and several players admitted they lost focus at times during that stretch. Coordinator Todd Wash has made consistency a focus during OTAs, and that’s going to be the biggest issue (other than staying healthy) in 2018. -- Michael DiRocco

Denver Broncos

2017 rank: Third

Major additions: OLB Bradley Chubb, CB Tramaine Brock, DE Clinton McDonald, S Su’a Cravens

Major losses: CB Aqib Talib, LB Corey Nelson

2018 outlook: Many of the Broncos' defensive statistics in 2017 were what the team has grown accustomed to in recent seasons, especially the 290 yards allowed per game and 89.4 yards rushing allowed per game. But the bottom line is they couldn’t get Von Miller free in the pass rush enough because opposing offenses weren't worried enough about anybody else in the formation to take the almost constant double- and triple-teams away from Miller. And their 29 touchdown passes allowed was a factor of both poor field position caused by their own offense’s turnovers, but also inconsistent red zone play. They believe they’ve addressed a major piece in that with the selection of Chubb at No. 5 in the draft. Chubb, as well as a healthy Shane Ray (he had three wrist surgeries last season), should give Miller more room to work, and he's poised for a huge year because of it. Bradley Roby has to be ready to replace Talib, who went to four Pro Bowls in his four seasons in Denver. The Broncos liked what they saw from Roby when Talib got tossed from one game for fighting with Michael Crabtree and was suspended for another in the wake of that fight. -- Jeff Legwold

Philadelphia Eagles

2017 NFL rank: Fourth

Major additions: DE Michael Bennett, DT Haloti Ngata

Major losses: DE Vinny Curry, CB Patrick Robinson, DT Beau Allen, LB Mychal Kendricks

2018 outlook: The Eagles’ defensive line -- one of their great strengths during the Super Bowl run -- has dealt with its share of turnover and injury this offseason. Curry and Allen are now in Tampa Bay, DT Tim Jernigan has a long road back following surgery to repair a herniated disk, and DE Brandon Graham is recovering from ankle surgery. The Eagles imported a pair of accomplished players in Bennett and Ngata to help fortify the front, though both are in the twilight of their careers and dealt with injuries of their own in 2017. Things will have to break right on the defensive line for the Eagles to experience a similar level of success as last year. Defensive coordinator Jim Schwartz will also have to find replacements for contributors Robinson and Kendricks. Robinson in particular played a critical role as the standout nickel corner. Fortunately for him, CB Sidney Jones (Achilles) is healthy and full of star potential. He should help stabilize the secondary. With a lot of miles on the odometer from last season and a few question marks hanging over this group, it wouldn’t be surprising if the defense took a half-step backward. But there’s enough talent here to keep the Eagles among the elite. -- Tim McManus

Pittsburgh Steelers

2017 NFL rank: Fifth

Major additions: S Morgan Burnett, LB Jon Bostic, S Terrell Edmunds

Major losses: LB Ryan Shazier, S Mike Mitchell, CB William Gay

2018 outlook: It’s hard to say the Steelers' defense is markedly better without Shazier, who was having an All-Pro season before undergoing spinal stabilization surgery in December. The rushing defense fell apart without him, giving up 133 yards per game on the ground in Weeks 13-17 and the playoffs. Free-agent addition Jon Bostic and backup Tyler Matakevich might be able to produce, but they won’t replace Shazier. Still, the Steelers have enough firepower to contend for a top-five defense yet again. They are well-stocked with pass-rushers, led by one of the league’s best defensive end duos in Cam Heyward and Stephon Tuitt. They apply consistent interior pressure. The Steelers are hoping for major jumps from outside linebackers T.J. Watt and Bud Dupree. Inside linebacker Vince Williams can build off his eight-sack campaign last year. And the secondary hasn’t been this deep in years. They have at least four capable corners and a first-round safety (Edmunds) who might have trouble seeing the field behind starters Burnett and Davis. And at 6-foot-2 and 217 pounds with 4.4 speed, Edmunds could grow into a dime linebacker in pass coverage. Since 2013, the Steelers have invested serious draft capital in the defense. That investment has paid off in overall improvement, but the cracks showed in big moments against New England and Jacksonville last season. Time to patch those up with a more consistent defense. -- Jeremy Fowler

One to watch in 2018

Los Angeles Rams

2017 NFL rank: 19th

Major additions: CB Marcus Peters, CB Aqib Talib, DT Ndamukong Suh, S Lamarcus Joyner (re-signed)

Major losses: CB Trumaine Johnson, DE Robert Quinn, LB Alec Ogletree

2018 outlook: The Rams took a win-now approach in the offseason, opting for the veteran trade market and free agency to add key pieces to Wade Phillips’ defensive unit. Yes, the lack of proven edge rushers and second-level defenders should be brought into this discussion. I get it. However, with the additions of cornerbacks Marcus Peters and Aqib Talib via trades -- along with placing the franchise tag on versatile safety Lamarcus Joyner -- the L.A. secondary looks legit. That’s a ball-hawking unit, a physical group with the ability to play man coverage, challenge routes and finish. Love it. Lock those receivers down and let the boys up front hunt the QB. Plus, with the Rams landing Ndamukong Suh in free agency, L.A. can pair the veteran defensive tackle with All-Pro Aaron Donald. That gives L.A. two disruptors in the middle of the defense who can also put those linebackers in a position to run free. Read, react and track the ball. And with Phillips pulling the strings in the game plan, the Rams can cater to their strengths to create turnovers, pressure and positive field position. The way I see it, this is a unit with the talent and the upside to make a sizable leap in 2018. -- Matt Bowen