Calais Campbell of the Jacksonville Jaguars has 12 1/2 sacks in 2017, the fourth most in the NFL. (Sam Greenwood/Getty Images)

The Jacksonville Jaguars, former cellar-dwellers of the AFC South who last made the playoffs after the 2007 season, are on the verge of making NFL history.

Heading into Week 15, the Jaguars lead the league in sacks (47), takeaways (30) and fewest points allowed (202). Should that hold for the remainder of the season, they will become the first team since the AFL-NFL merger in 1970 to lead the league in all three categories.

That’s a remarkable achievement.

The 1976 Pittsburgh Steelers, famously known as the “Steel Curtain” and the No. 1 defense on ESPN’s 2007 list of the top 10 NFL defenses of all time, ranked first in points allowed (138), fifth in takeaways (54) and 13th in sacks (41) that year. The No. 2 team on ESPN’s list, the 1985 Chicago Bears, ranked first in points allowed (198) and fifth in takeaways (46) but finished third in sacks (64) that year. The 2000 Baltimore Ravens, No. 3 on the list, ranked first in points allowed (165, an NFL record) and takeaways (49) but ended up with just 35 sacks for the year, placing them 22nd out of 31 teams. None of the four other defensive squads on the list playing since 1970 managed even a top five finish in each category.

Team Points allowed Takeaways Sacks
1976 Pittsburgh Steelers 1st 5th 13th
1985 Chicago Bears 1st 5th 3rd
2000 Baltimore Ravens 1st 1st 22nd
1971 Minnesota Vikings 1st 3rd 17th
1990 New York Giants 1st 8th 24th
1973 Miami Dolphins 1st 22nd 2nd
1975 Los Angeles Rams 1st 11th 5th

Gil Brandt, a senior analyst at and former executive for the Los Angeles Rams, San Francisco 49ers and Dallas Cowboys, offered an updated list of the top NFL defenses of all time in 2016, adding the 2015 Denver Broncos, 2013 Seattle Seahawks and the 1986 New York Giants to the league’s best defensive squads with a note that he also considered adding the 2002 Tampa Bay Buccaneers as well. Only one, the 1986 Giants featuring Hall of Famers Lawrence Taylor and Harry Carson, had top five finishes in all three categories.

Team Points allowed Takeaways Sacks
2015 Denver Broncos 4th 8th 1st
2013 Seattle Seahawks 1st 1st 8th
1986 New York Giants 2nd 4th 4th
2002 Tampa Bay Buccaneers 1st 3rd 6th

The NFL has obviously changed quite a bit since most of those teams suited up, but even after you compare the 2017 Jaguars to more recent teams with stellar defenses, they still come out on top.

Jacksonville’s defense is allowing a league-low 1.2 points per drive in 2017, but, more importantly, it has caused opposing offenses to score 13.1 points per game fewer than expected based on the down, distance and field position of each individual play of the drive. No other defense over the past 17 years has been more effective.

They are the best in the NFL, by a pretty good margin,” Seattle Seahawks Coach Pete Carroll said Wednesday about Jacksonville’s defense. “They’ve got a big rotation of guys who come after you, linebackers who can fly, a secondary with a bunch of ballhawks back there. They cause a lot of problems.”

The key for Jacksonville has been defensive coordinator Todd Wash’s ability to play to his team’s strengths. Using the Cover 3 scheme that made the 2013 Seahawks’ “Legion of Boom” so successful, with zone defenders underneath and corners playing man-to-man on the outside, Wash also uses more split-safety looks this year, which has freed up second-year cornerback Jalen Ramsey and five-year veteran A.J. Bouye to take more chances in coverage.

Those two have accounted for 10 of the team’s 19 interceptions and rank No. 2 and No. 4, respectively, out of 90 qualified corners by the game charters at Pro Football Focus for their skill in pass coverage this season.

“Normally, guys that can’t play receiver go to DB. That’s the joke offensively,” Jacksonville Coach Doug Marrone told reporters Monday. “But I think all of our guys could go play receiver. That’s a credit to them. They do have really good hands.”

Stellar coverage in the secondary allows Calais Campbell, recently named the mayor of Sacksonville, Yannick Ngakoue and Malik Jackson to wreak havoc along the four-man front. Campbell’s 12 1/2 sacks rank fourth in the NFL this season, earning him the seventh-highest grade among edge rushers from PFF in 2017. Ngakoue’s 11 sacks and league-leading six forced fumbles put him close behind in the PFF ratings at No. 13. Jackson, meanwhile, has set career highs in sacks (seven) and forced fumbles (three).

The overall result is a defense that is allowing a league-low 66.4 passer rating against in 2017, several points lower than the Ravens, who rank second (72.8). And if you can stop the pass, you can go a long way in the playoffs.

One of the most reliable indicators for separating the title contenders and pretenders is by looking at passer rating differential — the difference between a team’s passer rating and the collective rating of the team’s opposing quarterbacks. Its correlation to success led football stathead Kerry Byrne to dub it the “Mother of All Stats” during the 2012 Pro Football Researchers Association biennial meeting hosted by NFL Films. Since 2002, 22 of the past 30 Super Bowl participants had a passer rating differential among the top five in the league, including 10 of the past 15 winners. If the season ended today, the Jaguars would finish the season with a plus-19.1 net passer rating differential, fifth-best this year.