SANTA CLARA, Calif. -- As a young assistant coach for the Tampa Bay Buccaneers in his formative coaching years, Kyle Shanahan spent long days and late nights learning the NFL from every imaginable angle.
Many of those hours were spent drawing plays for the offense, but the time Shanahan valued most was sitting in on defensive staff meetings. Every day after practice, Shanahan learned the nuances of the Tampa-2 scheme from defensive coaching luminaries such as Monte Kiffin, Mike Tomlin, Rod Marinelli and Raheem Morris.
Even now, as the head coach of the San Francisco 49ers, Shanahan calls that time "the most important thing in my whole career."
Which is why it should be no surprise that Shanahan, known for his creative offensive mind, again has an elite defense. Through five weeks, a compelling argument could be made that the Niners are the league's best defense and, if they manage to stay close to current trajectory, one of the best in recent memory.
"We don't strive for second place in nothing," defensive lineman Kerry Hyder Jr. said. "So, whatever it is, we wanna be the best at it. That's our goal. We shoot for the stars and see where we land."
Before we get too far into the historical company the 49ers' defense has kept so far, some necessary caveats. Yes, it has been only five games. Yes, the Niners are going to face better offenses and quarterbacks as the season wears on. Yes, the defense has already dealt with injuries, which could derail a potentially special defensive season if they continue or worsen.
But it's worth recognizing that Shanahan, Lynch, defensive coordinator DeMeco Ryans and their respective staffs have built a deep group with few weaknesses when all (or most) key contributors are available.
Entering Sunday's game at the Atlanta Falcons (1 p.m. ET, Fox), the Niners rank first on a per-game basis in points allowed (12.2, tied with Buffalo), defensive efficiency (79.98), defensive expected points added (46.26), yards per rush (3.0), yards per play (4.01), yards per game (249.2), sacks per drop back (10.6%) and first downs allowed (15.8), among other categories.
Those numbers are impressive enough, but they're even more eye-opening when put in historical context.
Consider that since 2000:
Only the 2008 Pittsburgh Steelers have allowed fewer yards per play (3.90).
Two teams allowed fewer points per game, with the 2000 Baltimore Ravens setting the standard at 10.31.
Five teams have allowed fewer rushing yards per game, with the 2000 Ravens leading at 60.6.
Three teams have given up fewer yards per game, with the 2008 Steelers the best at 237.2.
Three teams yielded lower yards per rush, with the 2000 Ravens at 2.68.
The biggest challenge to keeping those numbers an elite level will be replacing cornerback Emmanuel Moseley, who tore his left ACL in Sunday's win over the Carolina Panthers. San Francisco coaches and players believe Moseley was turning into a Pro Bowl corner before the injury, and that pairing him with free-agent cornerback Charvarius Ward turned what was seen as a defensive weakness into a strength.
In 2021, the Niners were a good defense late in the year but struggled to find consistency because of the rotating door at corner opposite Moseley. The raw numbers weren't bad, but that group led the league in pass interference penalties and yardage, which skewed the final statistics.
In the offseason, Shanahan and general manager John Lynch prioritized bolstering that position, signing Ward to a three-year deal worth up to $42 million.
The early returns indicate Ward could be the best free-agent signing by any team in the offseason. Ward is second in the NFL in pass breakups with eight, including a career-high four against the Panthers on Sunday. According to NFL Next Gen Stats, he also ranks second among cornerbacks in passer rating against when the nearest defender (35.1), allowing a completion rate of 37.5%.
Having Ward, who is a strong tackler with good coverage skills, has allowed Ryans to evolve even more in his second year as coordinator and gives the 49ers some cushion with Moseley's injury. Ryans is increasingly adept at mixing up coverages and deploying blitzes and though he's not straying too far from his zone coverage or four-man pressure roots, he's finding better results because of the improvement on the back end. That should come in handy even with the loss of Moseley, with veteran corner Jason Verrett -- who starred in 2020 before missing all but one game in 2021 with a torn right ACL -- being a potential solution in time.
"The corners, I think that changes everything for our defense," Ryans said. "It's always about the edges of your defense. And when you have guys who can rush the passer on the edge, you have corners who can hold up on the edge, there's so much more that you can do and so much more freedom as a playcaller because you have confidence in those guys, the corners and the edge rushers.
"We have such a great group of guys that it really doesn't matter what the call is right now. Like those guys bring the call to life and that's what it's all about without these players. That's the story. It's not about DeMeco at all. It's all about the players and what they're able to do."
That's allowed the Niners to have success thus far regardless of coverage. They've played man on 31.5% of opponent drop backs (fifth lowest in the NFL) and are allowing a QBR of 19.6 on those snaps, which is third best. They're in zone on 68.5% of drop backs (sixth most) and allowing a QBR of 29.8 on those snaps, also third best.
That goes hand in hand with the ferocious pass rush that has been a priority since Shanahan and Lynch arrived in 2017. The Niners lead the league with 21 sacks, the most by the franchise in its first five games since 1998. In the past two weeks, they've posted 13, the Niners' most in a two-week span since the first two weeks of the 1985 season.
Despite their hot start, this defense believes there's far more to do.
"The thing about football is no game is perfect," Hyder said. "And so we can just strive for that perfect game."