They stop the run (second in the league) and defense the pass (77.7 passer rating allowed is fifth).
They get relentless pressure - 17 sacks, 101 quarterback hits, and 115 pressures, according to the tabulation of coaches - usually with just four rushers.
The 49ers have allowed just 16.2 points per game (second in the NFL to the Ravens), and are fourth in third-down efficiency (30.2 percent).
And they have done this facing four offenses ranked in the top half of the league, including the Cowboys (sixth), and the Eagles (third) and Lions (13th) on the road.
Oh, and did we mention the 49ers have done this with a new coaching staff after a lockout and with six new starters?
Not many thought that possible.
At the center of it all has been defensive coordinator Vic Fangio, who is finally getting his moment in the sun after 25 years as an assistant coach in the league.
“I think he’s one of the all-time best defensive coordinators in the history of the league,’’ said first-year head coach Jim Harbaugh. “I think that’s who he is. I think that’s what his legacy will be someday.’’
Fangio, 57, has been a defensive coordinator three times. But now he’s his own man.
He worked side-by-side with Packers defensive coordinator Dom Capers for 16 years, including eight as his coordinator with the Panthers (1995-98) and Texans (2002-05). But those were expansion teams, and they played Capers’s defense.
Fangio was coordinator for Jim Mora with the Colts from 1999-2001, but the talent was not very good. Mora felt so strongly that Fangio was not to blame that Mora refused general manager Bill Polian’s advice to fire him, so they were all let go.
Under Harbaugh, Fangio has finally been given free rein.
“He’s a real quiet guy,’’ said inside linebacker Patrick Willis. “He just says what needs to be said and not too much more. He keeps it simple and puts us in great position. We feed off of him.’’
Fangio is the first to admit that general manager Trent Baalke has assembled a lot of talent for Fangio to work with.
