San Francisco had the 23rd-best defense overall last year per Football Outsiders after adjusting its success on every single play for situation and opponent. The pass defense was the sixth-worst of 2018. This season the 49ers’ defense rocketed to No. 2 overall with the second-best pass defense in the NFL. And much of that improvement is due to Bosa, the first 49ers rookie to be named to the Pro Bowl since Patrick Willis in 2007.
Coach Kyle Shanahan and defensive coordinator Robert Saleh were able to use Bosa’s speed-to-power ability in their wide-9 technique to isolate offensive tackles in space. Specifically, the edge rusher lines up outside of the tight end (or offensive tackle if no tight end is on the line of scrimmage) at an angle facing the quarterback. This creates opportunities for the edge rushers to beat pass blockers with speed on the outside and for an interior defensive linemen, such as DeForest Buckner, to win one-on-one battles inside. If Buckner can occupy the opposing center and right guard, Bosa and the other edge rushers can more easily attack the quarterback.
The results speak for themselves. Four 49ers defensive linemen were credited with at least 6½ sacks in 2019: Arik Armstead (team-leading 10 sacks), Bosa (nine), DeForest Buckner (7½), and Dee Ford (6½). No other team had more than three players hit this milestone and last year just one 49er, Buckner, was credited with 6½ sacks or more.
The value of those sacks was enormous. San Francisco’s defense allowed 2.0 points per drive this season when the 49ers didn’t have a sack and only 0.5 points per drive when the team registered one sack or more, per data from TruMedia. The rate of opponents going three-and-out against them also improved from 33 to 47 percent.
Bosa, however, was more than just a sack machine. He was named the league’s rookie of the year after also registering 47 tackles (16 for a loss) with an interception, a forced fumble and two fumble recoveries. His 80 quarterback pressures (sacks, hits and hurries) were the sixth most among edge defenders, according to the game charters at Pro Football Focus, and the most by any NFL rookie pass rusher recorded by PFF. Bosa’s disruption rate was also consistent whether he lined up on the left or right side of the defensive line. And theoretically the wide-9 alignment, because it spreads out the defensive linemen along the line of scrimmage, is supposed to put Bosa at a disadvantage against the run. However, he made 20 stops against the run this year, the eighth-most among defensive ends playing in a 4-3 base defense.
Bosa’s domination isn’t limited to the regular season, either. He had two sacks, one quarterback hit and four hurries against the Vikings in the divisional round of the playoffs and even broke up a pass when he dropped into coverage.
“Obviously making the plays is good,” Bosa said on Wednesday. “But, I mean, I try to bring the same effort, same technique, same everything every week. [Sunday] I got a couple sacks. That always helps. But most of the plays that I’m most proud of are the plays that weren’t the sacks.”
Look for Bosa to have one of his toughest matchups of the season on Sunday against Green Bay’s David Bakhtiari, the fifth-best left tackle of 2019 per Pro Football Focus. Bakhtiari hasn’t allowed a sack since Week 9 of the regular season and he allowed no sacks or hits against Rodgers in Week 12 when they faced the 49ers. Packers right tackle Bryan Bulaga, the 10th-best player at the position this year per PFF, also played just nine snaps in that game before exiting with an injury, leaving backup Alex Light to fend off Bosa and the 49ers’ defensive front. Bulaga missed Sunday’s game against Seattle with an illness but he returned to practice on Wednesday.
“Just another really good tackle,” Bosa told reporters. “Whenever you’re a veteran, I feel like being a veteran at tackle is probably the most advantageous because just all the savvy little tricks they have. I mean, he’s faced tons of good rushers over the years, just like their left tackle. It’s going to be even more difficult with him on the field.”