Every NFL season from 2013 through 2016, the question of "who is the best defense in the league" basically boiled down to two teams: the Seattle Seahawks and the Denver Broncos. As we wrote last summer: 

No NFL team has allowed fewer yards or yards per play over the last four years than the Seahawks. The Broncos rank second in both categories. No NFL team has allowed fewer points, fewer first downs, a lower passing rating, or fewer yards per rush attempt. The Broncos rank seventh, seventh, third, and fourth in the same categories. No team has gotten more sacks or generated more pressures (sacks plus hits plus hurries) over those four years than the Broncos. The Seahawks rank in the top 10 in sacks and top five in pressure.

Seattle led the league in scoring defense every season from 2012 through 2015, and finished third in 2016. They led the NFL in yards allowed in 2013 and 2014 before finishing third in 2015 and fifth in 2016. The Broncos finished in the top five in yards allowed during each of the last three seasons. The Seahawks and Broncos are also the only two teams to finish in the No. 1 spot in Football Outsiders' defensive DVOA (Defense-adjusted Value Over Average, a performance efficiency metric that adjusts for down, distance, and opponent) at any time during the last four years. Seattle took the defensive DVOA crown in 2013 and 2014, while the Broncos took it home in both 2015 and 2016. 

Last season, an entirely new team emerged as the best defense in football: the Jacksonville Jaguars. I'd like to say it was so predictable that we actually predicted it, but the Jags didn't even make our list of four teams that could push the Seahawks and Broncos for the title of best defense in the league. This time around, let's rectify that. Below, you'll find the leading contenders for the NFL's best defense during the 2018 season. 

Jacksonville Jaguars

Led by elite groups up front and on the back end, the Jaguars finished the 2017 season second in both yards and points allowed, first in yards allowed per play, first in points allowed per drive, and first in Football Outsiders' defensive DVOA. Free-agent signings Calais Campbell and A.J. Bouye turned out to be possibly the two best signings of last year, as both players somehow emerged as Defensive Player of the Year candidates. Campbell finished second in the NFL with 14.5 sacks while Bouye held opposing quarterbacks to a pitiful 31.6 passer rating on throws in his direction. The crazy part is that it's entirely possible neither of them was the best player on Jacksonville's defense, thanks to the presence of Jalen Ramsey. All three are back in 2018, along with Malik Jackson, Yannick Ngakoue, Dante Fowler, Myles Jack, Telvin Smith, Barry Church, Tashaun Gipson, Abry Jones and Marcell Dareus. They lost slot corner Aaron Colvin to another team on this list, but they've got Jalen Myrick and D.J. Hayden ready to pick up the slack, and plenty of draft capital with which to add more depth at defensive back. These guys are going to be damn good once again. 

Los Angeles Rams

The Rams are certainly the team on this list that has made the biggest splash this offseason. The team's offense got most of the attention last season thanks to the emergence of Jared Goff, the re-breakout of Todd Gurley, and the creative play-calling of coach Sean McVay, but the defense might actually have been the better unit. The Rams finished the 2017 season seventh in points allowed per drive and sixth in defensive DVOA. Had Defensive Player of the Year Aaron Donald not held out long enough to miss the first two games of the year, those figures might've been even better. All the Rams have done this offseason is go out and get him a ton of help. First, they traded for star Chiefs cornerback Marcus Peters, who leads the NFL in interceptions since entering the league and has held opponents to a passer rating below 70 in each of his three seasons. Then, the Rams swung another trade for Aqib Talib, who may be on the wrong side of 30 and in the final year of his deal but is still a heck of a player. And on Monday, they pulled off one of the most impressive signings of the offseason, landing Ndamukong Suh on a one-year, $14 million deal. Let's go to defensive coordinator Wade Phillips for a reaction: 

Sure, the loss of Robert Quinn on the outside will hurt, but the Rams can make up for his absence by having the best group of interior rushmen in football as well as one of the NFL's best secondaries. It's safe to say Wade's going to have some fun with this crew. 

Minnesota Vikings

Remember how we mentioned earlier that the Jaguars finished last season second in both yards and points allowed? Well, these are the guys that finished first. In both categories. The Vikes also ranked second in yards allowed per play, points allowed per drive, and defensive DVOA. They were the only team in the league to finish in the top five in each of those categories, plus the top five in DVOA against both the run and the pass. Mike Zimmer is one of the best defensive coaches in the NFL, and he just got another fun toy to play with, as the Vikings signed former Jets and Seahawks star Sheldon Richardson on a one-year deal. Richardson should help mitigate the loss of interior stalwart Tom Johnson, and something tells me the Vikings will be OK getting by with just Linval Joseph, Everson Griffen, Danielle Hunter, Brian Robison, Anthony Barr, Eric Kendricks, Harrison Smith, Xavier Rhodes, Andrew Sendejo, and (assuming he comes back for one more year) Terence Newman

Philadelphia Eagles 

Speaking of teams that were awfully good defensively last year, that had a specific strength along the defensive line, and added one of the best defensive linemen in the league ... your Super Bowl champion Eagles would like to throw their hat in the ring. Like the Rams, Philly's offensive got most of the attention last season, but the defense was nothing to sneeze at. The Eagles finished fourth in yards and points allowed, sixth in yards allowed per play, third in points allowed per drive, and fifth in defensive DVOA. They swung a trade for former Seahawks star Michael Bennett this offseason (Bennett may face a suspension stemming from his recent felony arrest), helping them keep pace with the Vikings and Jaguars in the race for the best defensive line in the league. They lost breakout cornerback Patrick Robinson in free agency, but getting a full season from last year's second-round pick Sidney Jones, as well as last offseason's trade acquisition Ronald Darby, should help make up for that loss. And if the secondary takes a slight step backward, well, they Eagles still have one of the league's best front sevens to make up for it. 

Houston Texans

This one is a bit of a wild card considering the Texans finished last season dead last in scoring defense and just 20th in yards allowed. But that'll happen when two of your three best defensive players go down for the year with early-season injuries. A unit with a healthy J.J. Watt, Whitney Mercilus, and Jadeveon Clowney has to be on anyone's shortlist for best defense, and when you add in the fact that they signed Colvin away from the Jags and then added Tyrann Mathieu after that, well, there's just too much talent on this defense not to take them incredibly seriously. Assuming good health, they should be strong at all three levels and extremely tough against both the run and the pass.