Offense was king in 2018. If you were paying close enough attention, though, you might have noticed defenses came to life when we counted them out. In that legendary 54-51 Monday Night Football matchup between the Chiefs and Rams in November, the defenses combined to score three touchdowns, and the Rams won after their defense came up with back-to-back interceptions of Patrick Mahomes late in the fourth quarter.

On Sunday in New Orleans, in a game between two teams with nine Pro Bowl players on offense and just two on defense, the Saints-Steelers clash was decided by a defensive stop. Sheldon Rankins stripped JuJu Smith-Schuster of the ball during a potential game-tying drive from the Steelers, locking up the No. 1 seed in the NFC for the Saints and forcing the Steelers to seek help from the Browns to get into the playoffs in Week 17. (Defense just made me write something that would have seemed unfathomable before the season.)

Those aren't two isolated incidents, either. While it seemed like the NFL was sure to set scoring records midway through the 2018 season, point totals have fallen off around the league over the past month. If you thought this was becoming a league in which whoever held the ball last would win every week, well, you haven't been paying attention. Defenses still have a shot in today's NFL, and while everyone would prefer to have a franchise quarterback, there are teams that might give opposing offenses fits in the postseason without one.

Defense is back

It wasn't ever really gone, of course, but we've seen a defensive resurgence in the NFL over the past month. Through the first 12 weeks of the year, offenses were continually feasting on defenses that looked like they didn't have an answer. Teams were averaging 24.1 points per game, nearly a full point above the previous modern league record through 12 weeks, which was set at 23.3 points in 2013. Bolstered by the Chiefs-Rams game in Week 11, teams had averaged 24.4 points over the four-week stretch in November (Weeks 9-12).

There was no reason to think that scoring would fall precipitously over the ensuing month, but that's exactly what has happened. Even with the Chiefs and Seahawks combining for 69 points on Sunday night, NFL teams have averaged just 21.3 points per game from Weeks 13-16, with Monday Night Football still to come. In other words, scoring has fallen off by more than 12.2 percent over the past four weeks in comparison to the previous four weeks.

The Rams picked off three passes vs. Patrick Mahomes in their Week 11 win over the Chiefs, who committed five total turnovers. Photo by Robert Hanashiro/USA TODAY Sports

Nearly three points per team per game might not seem like all that much, but to put that in context, 12.2 percent represents the largest drop-off from one month to the next in scoring in 25 years, going all the way back to December 1993. It's tempting to point to colder weather and the quarterback attrition rate to suggest that scoring is likely to drop off as the season goes along, but from 1990 to 2017, the difference in points per game from Weeks 9-12 to Weeks 13-16 was minuscule. The second batch of games scored 99.9 percent as many points as the first. This is a weird, unexpected, nearly unprecedented drop-off.

What has changed?

I wanted to see whether there has been some noticeable difference in performance in what we've seen over the past four weeks as opposed to what was happening beforehand. Mostly, I found a steady decrease in most rate statistics across the board on offense. Offenses seem to be a little less efficient at just about everything. You might notice that teams have been averaging 10 more penalty yards per game, but that's mostly attributable to a one-week spike in offensive holding calls. Teams were penalized for an average of 76.4 yards per game in Week 13, when the holding emphasis was in place, compared to an average between 61 and 64 yards afterward.

NFL rate statistics over the last month pic.twitter.com/JTAKPa9ntn — Bill Barnwell (@billbarnwell) December 24, 2018

The one significant exception -- and the element of the game that has fallen off over the past month more than any other -- is that offenses aren't dominating when they throw downfield. The NFL defines deep passes as throws traveling 16 or more yards in the air. The passer rating on those throws has dropped off by nearly 20 points over the past month, and even that took a big game from Russell Wilson on Sunday night to get the mark within 20.

Again, while it might be instinctual to point toward inexperienced rookies like Josh Allen or hopeless backups like Brock Osweiler and Cody Kessler and suggest that they're dragging down the deep passing numbers, it's not the only issue. The guys who were great on deep passes over the first three months of the season have fallen back to earth over the past four weeks. Here are the top 10 qualified quarterbacks on deep throws by passer rating over the first 12 weeks of the season, and what they've done on those same throws over the past month:

These quarterbacks have seen their passer rating on deep throws fall by nearly 40 points. They threw 20 interceptions in 769 tries before Week 13, but with Philip Rivers and Jared Goff leading the way, they've tossed 15 picks on 288 attempts over the past month.

Is this some sinister plot from the league to dampen scoring? Have defenses suddenly figured out a solution to take away deep throws from the league's most devastating offenses? No and no. To one extent or another, this happens most years. In 2018, the passer rating on deep throws has fallen off by 18.3 points from Weeks 1-12 to Weeks 13-16. In 2017, it was 15.9 points. In 2016, it was 19.6 points. Passer rating actually increased over this same four-week span in 2015 and was roughly stagnant in 2014, but it declined by 10.2 points in 2013 and a whopping 24.7 points in 2012.

The average decline in passer rating on deep passes over the past 10 years from Weeks 1-12 to Weeks 13-16 is 10.5 points, and barring something I'm not seeing in the data, it likely owes more to tired quarterback arms and declining weather than anything else. The league's quarterbacks were better than they had ever been before on deep throws over the first three months of this season, which helped stoke a scoring boom. Over the past month, we've seen regression toward (and perhaps past) the mean. Their true level of performance -- and the league's scoring rate -- lie somewhere between the two extremes.

Who's winning with defense?

The old canard about how offense wins games and defense wins championships isn't borne out by reality. Good teams win championships, and those teams don't always have great defenses. The 2017 Patriots ranked 31st in DVOA and nearly won the Super Bowl, and while the Eagles had the better defense, they allowed the Patriots to score 33 points and rack up the most yards of any team in a loss in NFL history. The 2014 Patriots, meanwhile, beat the Legion of Boom Seahawks in Super Bowl XLIX. The 2012 Ravens, who were 19th in defensive DVOA, beat the 49ers (third) in Super Bowl XLVII. You get the idea.

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What is true, though, is that you can win with a transcendent defense and a middling offense. The 2015 Broncos were running on fumes on offense with Peyton Manning and turned things over to Brock Osweiler for a regular-season stretch before going back to Manning. Despite averaging just 254 yards per game while scoring a total of four offensive touchdowns in the postseason, the Broncos ran the table and won Super Bowl 50. The 2001 Ravens and 2003 Buccaneers loom as earlier examples of how to win with this model, but the Broncos proved that it remains feasible.

Who's actually relying on their defense this season? We can take a look at the win expectancy stats pieced together by ESPN Stats & Information to figure out which teams have been dominant. You can probably guess who leads the way:

Defensive win expectancy rank: No. 1

While Matt Nagy will rightfully get serious consideration for Coach of the Year, it's Vic Fangio's defense that is propelling the Bears into the postseason. The Bears rank first in defensive win expectancy but just 17th on offense and 22nd in win expectancy on passing plays. The only likely playoff team to get less out of its passing attack this season is the Ravens. The Bears are wedged between the Dolphins and Panthers in terms of passing win probability added.

Sunday was an example of how well Fangio's defense will need to play if the offense has a middling day in January. Mitchell Trubisky was 25-of-29 against the 49ers' defense, but just three of his completions traveled 8 or more yards in the air. The second-year quarterback didn't throw an interception, but Trubisky did make an awkward throw on a would-be pitch to Tarik Cohen that resulted in a fumble recovery for the 49ers and a short field. Cohen, who has been uncoverable for stretches this season, never got going and turned his seven touches into 19 yards. DeForest Buckner & Co. limited Trubisky to three rushing yards, and the Bears squeaked by with a 14-9 win. Allen Robinson even handed the Niners a late chance by fumbling away what should have been a game-icing catch in the fourth quarter.

In turn, the Bears' defense held their ground. They limited the 49ers to three field goals, all of which came in the second quarter. Most notably, they managed to hold the Niners on a drive that started on the Chicago 26-yard line after the Trubisky fumble. The opportunistic Bears defense was missing star safety Eddie Jackson, but when a fourth-quarter pass from Nick Mullens bounced off Marquise Goodwin's fingertips, Danny Trevathan pounced to grab the ball and take away a critical late scoring opportunity for the 49ers.

The Bears have the NFL's best defense, and they could still get a first-round bye in the playoffs. Cary Edmondson/USA TODAY Sports

Interceptions drive this defense. The Bears have picked off 4.6 percent of opposing pass attempts this season, most in the league. The Dolphins (4.1 percent) are the only other team above 3.1 percent this season. The Bears have 27 interceptions on 582 pass attempts; if they had the third-highest interception rate in the league this year (that of the Patriots at 3.1 percent), they would have only 18 picks.

When a team is such a dramatic outlier in one element of its game, I always wonder whether it's sustainable. I went back through 1990 and found that the Bears have the 31st-ranked interception rate for a playoff team over the past 28 years, which is impressive given that interceptions are harder to come by now than ever before. I wanted to see whether the 30 teams preceding the Bears kept their interception rate up come January and February.

They didn't, but the drop-off shouldn't worry Chicago fans. Those teams posted an average interception rate of 5.2 percent during the regular season, but against typically superior passing in the postseason, their interception rate fell by a full point to 4.2 percent, or nearly 20 percent. If you pushed that same sort of rate of decline onto the 2018 Bears, they would be picking off 3.7 percent of passes in the postseason. That would be just fine.

For the Bears to advance far into January, it's more important for Trubisky to be safe than good. Chicago played only four games against playoff teams this season, and while it went 3-1 in those games, Trubisky threw a combined nine interceptions while posting a 63.2 passer rating. He did run for 171 yards and 11 first downs in those games, but multiturnover games reduce Chicago's margin for error and force the defense to play at a transcendent level.

They were able to overcome those interceptions and beat the Rams in Chicago by forcing Jared Goff to throw four picks, but if Trubisky throws multiple interceptions against the Saints in the Superdome, will the Bears be able to shut down Drew Brees in a potential NFC Championship Game? Manning turned the ball over three times in three games during that final run to the Super Bowl; if Trubisky can keep his giveaways down, the Bears have a defense capable of winning games.

Defensive win expectancy rank: No. 2

Trubisky and the Bears have already clinched the NFC North and will be spending their Week 17 rematch against the Vikings hoping to earn a first-round bye, which would take a win over Minnesota and an unlikely 49ers win over the Rams. The game is more meaningful for the Vikings, who still need a result to make the playoffs. They would clinch a return trip to the postseason by either beating or tying the Bears. Mike Zimmer's team would also get in if Washington beats the Eagles in that classic Josh Johnson-Nick Foles matchup.

If you want to talk about sustainability, well, the Vikings are kicking sustainability in the teeth. The 2017 Vikings were the best third-down defense over the past 18 years (for which there is play-by-play data), allowing opponents a 25.2 percent conversion rate. The Vikings have regressed this season and fallen all the way down to ... the third-best third-down defense since 2001, allowing opponents to convert only 28.4 percent of the time. To be fair, if you include fourth-down conversions, the gap gets bigger -- the 2017 Vikings are at 26.9 percent, and the 2018 team is at 30.4 percent -- but this is still an absolutely scary defense to see when you need a third down.

The Vikings' 50 sacks this season are the most in the league. AP Photo/Jose Juarez

Things didn't go well for the Vikings on defense last postseason, when they allowed Brees and Foles to convert 52.2 percent of their third-down tries. I'd be worried about the third-down defense holding up again in 2018. Their most likely first-round opponent is the Bears, who have Trubisky as a devastating scrambler on third downs. He has converted 15 third downs with his feet, tying him for third in the NFL behind Cam Newton and Ezekiel Elliott. Their next game would be against the Saints, who are converting on nearly 45 percent of their third downs and went 4-for-9 against the Vikings on third down earlier this season.

The Vikings need more from their offense than the Bears do to thrive in January. On paper, that shouldn't be an issue. In practice? It is. Minnesota has scored 68 points over the past two weeks since firing offensive coordinator John DeFilippo and replacing him with quarterbacks coach Kevin Stefanski, but the offense has been wildly inconsistent. The Vikings marched down the field in Week 15 and scored touchdowns on their first three drives by picking on overmatched cornerback Bobby McCain, but the Dolphins then responded with a pick-six on a Kirk Cousins screen and held Minnesota to one first down over five drives before Cousins got going again.

Facing the lowly Lions on Sunday, Minnesota's offense went totally cold again and failed to pick up a single first down on its first four possessions. On its fifth drive, Vikings receivers managed to get called for holding twice, but Cousins overcame that with a 40-yard pass to Adam Thielen on third-and-18 before Stefon Diggs scored. Kyle Rudolph caught a Hail Mary for a touchdown on the next possession before halftime, and the Vikings added 13 more points after the break.

The Vikings badly need consistency. They can't go four drives without a first down in the playoffs and ask their defense to keep them afloat in Chicago, let alone New Orleans or Los Angeles. DeFilippo never seemed to click with Zimmer, and he might not have been a great fit for what the head coach wants his offense to do, but the move might have come too late in the season for the Vikings to find a rhythm under Stefanski.

Defensive win expectancy rank: No. 6

The Titans rank behind the Chargers (fourth) among the likely playoff contenders, but I'm going to throw them in here as the third squad of the bunch because they're getting hot. As scoring has come down over the past month, no team has inhibited the opposing offense more than Mike Vrabel's Titans. Tennessee has allowed a league-low 47 points over the past four weeks while ranking second in defensive win expectancy behind only the Jags.

The defense has helped save Tennessee's season, which looked to be lagging when the Titans lost by multiple scores to the Colts and Texans in consecutive weeks and fell to 5-6. Marcus Mariota led a furious comeback while down nine points in the fourth quarter to the Jets and triggered a four-game winning streak, although he left Saturday's victory over Washington with a stinger before halftime and was unable to return.

I'd be concerned that win expectancy isn't accurately measuring the degree of difficulty for the Titans here. During their four-game winning streak, the defense has actually allowed only 40 points -- one of the Jets' scores came on a pick-six. Ten points per game allowed is impressive, but consider who the Titans were playing. In Week 13, they faced Josh McCown. In Week 14, they got Cody Kessler on a short week. In Week 15, they were up against Eli Manning without Odell Beckham Jr. Then, on Saturday, the Titans faced Washington fourth-stringer Josh Johnson and a patchwork group of weapons and offensive linemen around the journeyman. Those offenses aren't very scary at 100 percent. Tennessee hasn't played any team close to 100 percent in a month.

Kevin Byard has four interceptions this season, including one in each of the past two games. AP Photo/James Kenney

To be fair, there have been genuine signs of growth. Malcolm Butler was a disaster during the first half of the season, but Butler has looked like he belongs as a starter as the season has gone on. (With Logan Ryan now done for the year, the Titans don't really have a choice.) The Titans are holding opposing receivers to the league's third-fewest average yards after the catch over the past month and are third in yards allowed to receivers after first contact. They've come up with three red zone stops and allowed just two touchdowns in nine tries; that's not sustainable, but they ranked fifth in red zone efficiency on defense even before this four-game winning streak.

Honestly, I don't think we know a ton about the Titans, even after this winning streak. If they really have shored up on defense, they can win playoff games by chewing up clock with Derrick Henry and holding opposing offenses to punts and field goals, and they didn't even need to do the latter to come back against the Chiefs in the playoffs last season.

I don't know how we can draw much insight into their defense given the replacement-level quarterbacks and offensive talent they've faced over this run. It wouldn't surprise me if they went up against Andrew Luck in the final regular-season game of the year and looked like a much worse unit, if only because of the dramatic shift in degree of difficulty. It also wouldn't surprise me if the Titans pieced together a totally coherent, effective performance when they needed one most. Vrabel's team is among the most frustrating, inconsistent teams in football. I also suspect that if they win on Sunday and make it back into the postseason, nobody will care about their regular-season missteps.