Not so long ago, it was fairly easy to categorize NFL defenses as 3-4 or 4-3, depending on the coordinator's scheme and how many players he deployed at the line of scrimmage. In recent years, though, there's been a shift toward hybrid schemes that allow defenses to alter alignments based on their understanding of the offense's intentions in each specific situation.
That evolution has added a layer of complexity to linebacker evaluations, as bone-jarring run stuffers often give way to rangier coverage specialists or even cornerbacks and safeties in passing situations. Off-the-ball linebackers in 4-3 defenses, particularly, are perennially underappreciated in Pro Bowl and All-Pro balloting.
Even in a time of transition, this past offseason stands out as a jarring one for linebacker corps. Between defections, injuries, retirements and suspensions, the best front sevens in the NFL are under construction.
The Panthers will be without Pro Bowler Thomas Davis for the first four games. The Bengals are dealing with Vontaze Burfict's annual September absence. The Seahawks have to cover for K.J. Wright until he returns from knee surgery. The Jaguars are filling Paul Posluszny's shoes with a seventh-round rookie. The Titans are waiting for rookies Harold Landry and Rashaan Evans to get healthy and up to speed.
Perhaps no team better encapsulates the uncertainty at linebacker than the Steelers. Mike Tomlin's defense collapsed down the stretch last year when Ryan Shazier went down with a career-threatening spinal injury. One of the better linebacker groups in the league suddenly looks vulnerable, with defined roles for limited holdovers Bud Dupree (run stuffer), T.J. Watt (coverage specialist) and Vince Williams (blitzer).
As we embark on the 2018 season, teams such as the Cardinals, Colts and Raiders are adjusting to 4-3 schemes -- just as clubs featuring 3-4 schemes such as the Steelers, Chiefs, Rams and Giants are trying to patch holes. That goes a long way toward explaining why the Bears can skyrocket up the rankings with an early September blockbuster.
Here is how we rank the best linebacker units in the league:
1) Denver Broncos
Notables: Von Miller, Bradley Chubb, Brandon Marshall, Todd Davis, Shaquil Barrett, Shane Ray, Josey Jewell.
Analysis: The Broncos have it all. With the addition of Chubb, the No. 5 overall draft pick, it is one of the few defenses that can boast a pair of bookend pass rushers with game-wrecking potential. In Barrett and Ray, there's quality depth. To the underrated inside duo of Marshall and Davis, Denver added a promising rookie in Jewell. This defense might not be quite as dominant as the one that delivered the Lombardi Trophy in Super Bowl 50, but it could be one of the most improved units in the league.
2) Chicago Bears
Notables: Khalil Mack, Leonard Floyd, Roquan Smith, Danny Trevathan, Nick Kwiatkoski, Aaron Lynch.
Analysis: Even before the earth-shattering Mack trade, the Bears had an intriguing defense with Butkus Award winner Smith joining Trevathan and Floyd at linebacker. The big question was whether savvy coordinator Vic Fangio could fix his pass-rushing problems by reuniting with Lynch, whom he coached with the 49ers in 2014, and resuscitating his career. Now that Mack is on board, Chicago is a dark horse candidate to emerge as the NFL's top defense.
3) Carolina Panthers
Notables: Luke Kuechly, Thomas Davis, Shaq Thompson, David Mayo, Ben Jacobs, Jermaine Carter.
Analysis: Kuechly is a future Hall of Famer if he stays healthy. Thompson is ascending just as Davis reaches his decline phase, ensuring that the Panthers have two quality linebackers on the field at all times. Carter, a rookie, looms as a wild card on the heels of a promising preseason performance.
4) Seattle Seahawks
Notables: Bobby Wagner, K.J. Wright, Barkevious Mingo, Shaquem Griffin, Jake Martin.
Analysis: In the discussion for Defensive Player of the Year honors most seasons, Wagner is Kuechly's chief competition as the game's premier middle linebacker. The ideal weakside 'backer in Pete Carroll's system, Wright is recovering from an August knee scope. Fifth-round rookie Griffin, one of the best stories in sports, will fill in as the starter while Wright is out. Mingo and Martin are slated for the old Bruce Irvin role as edge-rushing specialists.
5) Houston Texans
Notables: Jadeveon Clowney, Whitney Mercilus, Benardrick McKinney, Zach Cunningham.
Analysis: Credit Houston with a smart succession plan for Brian Cushing at inside linebacker, drafting McKinney in 2015 and Cunningham in 2017. As solid as that duo might be, this linebacking corps rises and falls with the health of Clowney and Mercilus. The latter racked up 19.5 sacks in 2015 and 2016, only to have his 2017 season ruined by a torn pectoral muscle. Clowney finally made good on his prodigious potential with an All-Pro-caliber campaign but is coming off a knee scope of his own.
6) Minnesota Vikings
Notables: Anthony Barr, Eric Kendricks, Ben Gedeon.
Analysis: While Barr has been honored with three consecutive Pro Bowl selections, it's leading tackler Kendricks who is the heartbeat of Mike Zimmer's defense. Limited to early downs as a fourth-round rookie last season, Gedeon showed promise against the run. This is one of the few defenses that can feature high-octane units at every level, from the defensive line to the secondary.
7) Baltimore Ravens
Notables: Terrell Suggs, Matt Judon, C.J. Mosley, Patrick Onwuasor, Tim Williams, Za'Darius Smith, Kenny Young.
Analysis: Resistant to Father Time, Suggs remains one of the league's top all-around outside linebackers at age 35. Judon flashes pass-rushing potential that suggests double-digit sacks in his future. Don't sleep on 2017 third-round pick Williams, who turned heads in August. Mosley is one of the best inside linebackers in football, according to no less of an authority than Ray Lewis. Try as they might, the Ravens can't keep Onwuasor out of the lineup.
8) Jacksonville Jaguars
Notables: Telvin Smith, Myles Jack, Leon Jacobs.
Analysis: Smith is the headliner as a Pro Bowler with incredible range and closing speed. Jack improved throughout last season, emerging as a playmaker as well as a tight end's worst nightmare in coverage. He's moving to the middle this year, replacing franchise legend Posluszny. That opens up the weak side for Jacobs, an athletic seventh-round rookie who has caught on quickly.
9) Washington Redskins
Notables: Ryan Kerrigan, Preston Smith, Zach Brown, Mason Foster, Pernell McPhee, Ryan Anderson.
Analysis: Kerrigan is coming off the best season of his extraordinarily underrated career. He and Smith were one of the few tandems to combine for more than 20 sacks last season. A talented but frustrating tease early in his career with the Titans, Brown has developed into a fierce run stuffer on the inside.
10) Cleveland Browns
Notables: Jamie Collins, Joe Schobert, Christian Kirksey, Genard Avery.
Analysis: This unit took a hit when former Eagles linebacker Mychal Kendricks was charged with insider trading and subsequently released. What's left over isn't too shabby. A boon to the Browns' previously woebegone run defense, Schobert tied for the NFL lead in tackles as a first-time starter last year. Collins is a bounceback candidate after injuries derailed his first full season in Cleveland.
Follow Chris Wesseling on Twitter @ChrisWesseling.