NFL's top nine defenses in 2020: Chargers, Bills, 49ers all loaded, but who's No. 1?

I've been hot on this unit all offseason. Gus Bradley's a tremendous defensive coordinator, and the man has a wealth of talent -- on all three levels -- at his disposal.

It all begins with Derwin James, who burst on the scene as a rookie in 2018 -- earning first-team All-Pro honors with 98 tackles, 3.5 sacks, 3 picks and 13 passes defensed -- only to have his 2019 campaign largely wiped out by an offseason foot injury. Now the safety's back to full health, and this is everything for the Bolts. L.A.'s secondary is loaded and highly versatile -- with free-agent addition Chris Harris Jr. joining multi-talented cover men Casey Hayward and Desmond King -- but James is the straw who stirs the drink. The Swiss Army Knife of the unit, James is a playmaking star who contributes to every single component of this defense, from the pass rush to run support to coverage. His injury last August let the air out of this group's proverbial balloon. How impactful is No. 33? Well, as detailed in a "bold predictions" Schein Nine earlier this offseason, I could see James winning the 2020 Defensive Player of the Year award. He's that dynamic. And the back end isn't the only imposing level of this defense.

I loved the Kenneth Murray pick in April's draft. The first-rounder sounds like the total package at linebacker: a tone-setter with all the tangibles and intangibles you'd want. And he steps into a pretty ideal situation as a rookie MLB, with the aforementioned coverage group in the back end and a terrific tandem rushing the passer up front. Joey Bosa and Melvin Ingram offer premium juice off the edges. Bosa's a bona fide star, completely worthy of his new $135 million contract. Only one problem: Now Ingram wants more loot. That's a first world problem GM Tom Telesco will have to smooth over.

Philip Rivers has left the building, but the Chargers' defense is chock-full of established talent. Look for Bradley to field a dominant unit.

I love Sean McDermott. He's a gem of a head coach, completely transforming the Bills' culture during his three seasons on the job. Not to mention, he's a sensational defensive mind, with fingerprints all over the unit that quietly finished last season ranked second in scoring defense and third in total D. No wonder Buffalo just extended him through 2025. And McDermott's right-hand man, former head coach Leslie Frazier, is a luxury to have as a defensive coordinator.

Personnel wise, the Bills have two spectacular young building blocks: 25-year-old Tre'Davious White and 22-year-old Tremaine Edmunds. White just earned first-team All-Pro honors with an NFL-high six picks, while Edmunds made his first Pro Bowl as an emerging second-level dynamo. Meanwhile, the safety combo of Jordan Poyer and Micah Hyde remains criminally underrated, while DT Ed Oliver could be due for a second-year breakout. The talent is strong on every level. There's no weakness. And while the signings of veterans like Mario Addison, Vernon Butler, Josh Norman, Quinton Jefferson and A.J. Klein don't generate headlines, they fuel McDermott's system. The coaching takes this defense to the next level.

They traded DeForest Buckner ... and yet still possess the best defensive line in the game. Nick Bosa is an absolute freak. The reigning Defensive Rookie of the Year has a Defensive Player of the Year in his future. He just broke Pro Football Focus' record for total pressures from a rookie and then racked up four sacks in three playoff games. I loved the re-upping of Arik Armstead, a versatile D-lineman with length and strength who broke out with 10 sacks last year. The Niners, of course, used the first-round pick acquired via the Buckner deal on DT Javon Kinlaw, a perfect replacement for Buckner who's already turning teammates' heads as "a man amongst boys" during camp. And I haven't even mentioned QB hunter Dee Ford, who could end up being the fourth-best D-lineman on this team.

Behind this stacked D-line, Fred Warner is emerging as one of the best three-down linebackers in the game today, possessing the kind of coverage skills every team is looking for at the position. The biggest question area is the secondary. Richard Sherman somehow still played at a Hall of Fame level last year, but he's entering his age-32 season at a position that's not kind to the aging process. Safety Jimmie Ward's fresh off a breakout campaign, though. And defensive coordinator Robert Saleh is a master motivator who'll be a head coach soon.

This defense is so consistent and sturdy all around. No one embodies this more than 10th-year veteran Cam Heyward, who definitely deserves a new contract. I voted him first-team All-Pro last season, an honor that he did indeed receive for the second time in the past three years. Meanwhile, splash-play extraordinaire T.J. Watt was just named first-team All-Pro, as well, racking up 14.5 sacks, eight forced fumbles and 36 QB hits. With Stephon Tuitt returning from injury and Bud Dupree looking to earn big bucks while on the franchise tag, Pittsburgh's defensive front is quite a collection of talent.

On the second level, second-year linebacker Devin Bush is a sideline-to-sideline playmaker. He was put on planet Earth to be a Steelers linebacker. And in the back end, Minkah Fitzpatrick outstripped all expectations after his midseason trade from Miami, becoming the third member of this defense to nab first-team All-Pro honors in 2019. And with experience in Pittsburgh's system, he's primed to be even better in 2020, which is scary.

The defensive backfield is simply phenomenal. Marcus Peters was reborn after a midseason trade to Baltimore, which is why the Ravens rewarded him with a three-year, $42 million extension in December. And Peters wasn't the only Ravens corner to earn first-team All-Pro honors -- Marlon Humphrey also got the nod after a fantastic Year 3. When healthy, Jimmy Smith is so much more than the CB3 role he currently holds in Baltimore -- what a luxury for the Ravens. And Earl Thomas remains a stud in center field.

In the front seven, Matthew Judon can flat out ball -- and playing on the franchise tag, he'll be quite motivated to build his market for next offseason. Baltimore further bolstered the stout defense with a pair of high-impact offseason acquisitions. Hulking DL Calais Campbell is a perfect fit for the Ravens, on the field and in the locker room. Athletic LB Patrick Queen, the Ravens' first-round pick at No. 28 overall, made my list of rookies I can't wait to see.

All offseason, the focus has been on Tampa Bay's offense. Not surprising, as the Buccaneers did, after all, add the greatest quarterback and tight end in NFL history. But people need to stop sleeping on this defense's immense potential. Here's hoping that changes in 2020, with all eyes on Tom Brady's team.

The unit really came into its own during the back half of last season, when the young secondary started to settle in. Cornerbacks Carlton Davis, Sean Murphy-Bunting and Jamel Dean -- all still just 23 years old -- showed promise down the stretch. And now they're joined in the secondary by rookie second-rounder Antoine Winfield Jr., an exciting playmaker with an instant-impact pedigree. Meanwhile, Lavonte David remains chronically underrated and underappreciated. He's everything you want in a modern linebacker. And his partner on the second level, 2019 first-rounder Devin White, lived up to the billing in Year 1 and should take another step in 2020. The pass rush is fierce, with Shaq Barrett and Jason Pierre-Paul hunting off the edges, while DTs Vita Vea and Ndamukong Suh form a brick wall in the middle, giving Tampa the top-ranked rush defense in 2019.

If the young corners can build off their progress from last season, Tampa's D will be much more than the Buccaneers' other unit.

Too high? Heck no! Chris Jones is a force inside. Frank Clark is an edge menace. Tyrann Mathieu is a leader and a playmaker. Steve Spagnuolo is a fabulous defensive coordinator.

Look at how Kansas City's defense played down the stretch and in the playoffs last year. Chiefs defenders made plays to get the ball back to Patrick Mahomes. And really, that's how this defense will be defined.

Truth is, this defense just wasn't the same after Vic Fangio left to coach the Broncos. Truth is, Khalil Mack had a down year in 2019.

That said, I'm still a believer in this unit because I'm still a believer in the 29-year-old Mack. I see him wrecking games once again in 2020, especially with Akiem Hicks back to good health and free-agent signee Robert Quinn joining the fray. Mack failed to reach double-digit sacks last season for the first time since his rookie campaign. I do not see that happening again.

And when Chicago's front applies the pressure, CB Kyle Fuller and S Eddie Jackson are there to make plays in the back end.

Cam Jordan is one of the very best defensive linemen in the NFL today, having just posted 15.5 sacks and earned his fifth Pro Bowl nod. The guy is a versatile force of nature who strikes fear in opposing offenses. With better health luck, Marcus Davenport could emerge as New Orleans' much-needed second pass rusher. The third-year pro has the talent -- he just needs to put it all together. Getting back a healthy Sheldon Rankins is huge, too. The 2016 first-rounder is an interior disruptor against the run and pass. Having Davenport and Rankins to complement Jordan is vital to the NOLA D.

Linebacker Demario Davis is finally getting the credit he deserves, having just been named first-team All-Pro after a dynamic 2019 campaign. Marshon Lattimore has been a bit inconsistent since his excellent Defensive Rookie of the Year campaign, but he just made his second Pro Bowl in three NFL seasons. I trust DC Dennis Allen to get the most out of his talented corner -- and a healthier Saints defense -- in 2020.