The San Francisco 49ers had a scorching start to the 2019 NFL season, going undefeated thru the first half of the campaign (en route to a 13-3 finish that landed them the NFC’s top playoff seed) for a variety of reasons; a lot of different folks deserve a lot of credit for that. But one element in particular stands out: the pass defense. Specifically, the mathematical relationship that was formed when you marry their devastating pass rush crushing opposing quarterbacks before they have a chance to throw, with their historically stingy coverage on the back end.

Defensive tackle DeForest Buckner is the focal point of it all, the engine that drives the supremely well-oiled machine, and an absolutely unblockable wrecking ball who led their defensive front. His collegiate teammate, Arik Armstead, has erupted as another interior disruptor in a contract year to further make life miserable up the gut for quarterbacks. Then screaming off the edge are prized trade acquisition, Pro Bowler Dee Ford, as well as the second overall pick in the 2019 draft: Nick Bosa.

Bosa instantly became as deadly an edge rusher as there was in the league from the moment he walked through the door, and would’ve been the first player to ever notch eight sacks through his first seven career games were it not for officials failing to realize Baker Mayfield’s knee was down prior to this intentional grounding (sparking Bosa’s tremendous flag-wave-and-plant celebration to settle a collegiate score with Mayfield):

And in the first half of the 2019 season (before injuries struck some key defenders), the 49ers sacked quarterbacks 30 times, resulting in a loss of 248 yards. At the same time, they allowed a gross total of just 1,353 passing yards. In other words, when attempting to pass against the 49ers defense, teams have gone backward for 18.3 percent of the yardage that they’ve gone forward. No other team defense in the last 30 years has ever generated a combination of sack yardage and lack of passing yardage allowed that’s even come particularly close at the same point in the season:

Their first four October games saw their pass defense rise to supernova levels that relegated opposing passing games to something resembling the days of caveman, three-yards-and-a-cloud-of-dust football ... with no one else even in their solar system.

After Week 3, a couple changes shook up their secondary. One defensive back, free safety Jimmie Ward, returned from a broken finger. Another, Emmanuel Moseley, stepped into the starting lineup at right cornerback in the wake of a foot injury suffered by rising youngster Ahkello Witherspoon.

The new-look unit’s first game was under the lights on Monday night — that aforementioned Browns game in which Mayfield threw for just 100 yards with Odell Beckham Jr. tacking on 20 to finish with 120 as a team. They absorbed 35 percent of that total on losses when four Mayfield sacks backed them up 42 yards.

Then on a short week in LA against the defending conference champion Rams who were coming off a long week, they utterly manhandled Jared Goff. He mustered a pitiful 78 passing yards (which produced a grand total of one first down) whilst going in reverse for 38.5 percent (30 yards) of that total on another four Niner sacks.

A muddy trip to D.C. followed for a matchup with a Washington passing game that never even get out of bed. Quarterback Case Keenum barfed out 77 passing yards, with three sacks pushing them back for 35.1 percent (27 yards) of that figure.

And finally, they then welcomed the Carolina Panthers to town to face a quarterback in Kyle Allen, who’d yet to lose a ballgame in five career starts. Allen’s passing moved ‘em forward for 158 yards, buuut got pulverized for seven sacks which moved ‘em backward for 36.7 percent (58 yards) of that.

That’s four consecutive games where the 49ers’ defense generated at least 35 percent as much sack yardage as they did passing yardage allowed. In the past 30 years, there have only been two other such streaks of any length, and they barely even amounted to streaks:

On a cumulative basis, they allowed opposing passers to rack up 433 yards across that four-game stretch, while sacks resulted in a loss of 157 yards. That is 36.3 percent. Some context:

Then on Halloween, Kyler Murray was able to pass for 241 yards while being sacked for ‘only’ 15.4 percent of said total. Thus when you extend the sample to the entirety of October, that figure drops to 28.8 percent; in the 21st century no one but the ‘06 Ravens has had a five-game stretch with such a percentage even reaching 19:

And a lot of those are from the early ‘90s, so it really is even more of an outlier among just the past 20-25 years given the reality of the passing game’s evolution over that time. For instance, in 2019, here’s how the fact they managed four of those 35-percent games stacks up:

During that four-game October symphony of crushing aerial attacks, those destructions of Goff and Keenum represented the only time in the past 30 years a defense has allowed no more than 50 net passing yards (sack yardage subtracted from passing yardage allowed) in back-to-back games. In fact, no one else in that time has had back-to-back games allowing fewer than 60 net passing yards.

The Niners failed to allow more than 100 in any of the four either, with only a couple other streaks in the last 30 years to even reach three games:

Combining that lack of quarterback success downfield with all those sacks and yards lost, across those four games they allowed just 276 net passing yards. Not only has no one in the past three decades allowed sub-300 across any four-game stretch, here are the only instances of even sub-400:

The rate at which teams have found themselves moving backwards compared to forward when dropping back to throw is one that hasn’t even been sniffed in the modern era. It’s a helluva tax to pay for trying to pass the ball against the 2019 49ers.