Admittedly, there's luck involved. But generally speaking, the dominance of the 49ers run defense comes down to the fundamental staples of football: desire and good, old-fashioned play.
The 49ers have not allowed a rushing touchdown all season and haven't allowed a single 100-yard rusher in 33 contests.
No question, it takes supreme talent to do that.
But as 49ers defensive coordinator Vic Fangio pointed out on Thursday, there's a little luck involved with the defense's relentless effort and sound technique.
Are this year's 49ers the best run defense Fangio's ever coached in his 25 seasons coaching in the NFL?
"I don't know if it's the best," Fangio said in his weekly press conference at team headquarters in Santa Clara. "I've been around some good ones, too. But it's damn near close. We just have good players."
Not since the 1928 Providence Steamrollers has a NFL defense gone 11 games without allowing a touchdown like the 49ers have done in their first year under Fangio's guidance.
"Obviously, having allowed none is unusual," Fangio admitted. "I don't even know where that is historically, you guys probably know. Some luck is involved, but its good play."
But the 49ers coordinator doesn't just have a front seven committed to stopping the run; his entire defense takes pride in shutting down the opposition's running attack. That fact alone is not lost on Fangio, who's overseen a defensive unit that leads the NFL in rushing yards (75.5) and points (14.6) allowed per game.
"I'll tell you the part that's overlooked in that, it's the defensive backs that've made some critical tackles that would have been touchdowns," Fangio stressed. "That's not to be lost in the discussion either."
Most will remember C.J. Spillman's tackle against the Baltimore Ravens last week, the one where the reserve 49ers safety knocked Ray Rice back for a four-yard loss when Baltimore was second-and-goal at San Francisco's 1-yard line.
Truth be told, the 49ers have had plenty of big tackles delivered by members of the secondary throughout the season.
"It's team thing," said safety Dashon Goldson, who's 54 tackles rank sixth on the 49ers defense. "In the defense we have, we have run fits. So when your number is called, you have to be accountable to make those tackles like the linebackers and D-linemen. You have gap control just like they do."
Following the lead of the front seven and hard-hitting safety combination of Goldson and strong safety Donte Whitner, the 49ers cornerbacks have equally made a point of getting involved against the run.
Carlos Rogers, who leads the team with five interceptions, takes just as much pride in laying a big hit as he does intercepting a quarterback. To him, it's all about being a well-rounded player.
"I take a lot of pride in tackling," stressed the seven-year veteran who's made 40 tackles already this year. "Picks are an outstanding thing. As a defensive back, it's what everyone looks at. But tackling, big hits, even a big breakup on third down, those are just as big."
Rogers even joked to teammates recently that he was hopeful of soon picking up his first career sack.
Overshadowed by one of the best front sevens in the game today, members of the 49ers secondary deserve credit for the dominance against the run.
Nose tackle Isaac Sopoaga, whom Fangio praised for his toughness and overall contributions to the defense, only needed two words to describe his teammates on the back end of the defense.
"Solid guys," Sopoaga said. "That's the best way I can explain it. They're doing a tremendous job in the backfield."
Keeping individual rushers under 100 yards falls on the entire defense. Same goes for the no rushing touchdowns allowed.
"I know the other 10 guys on the field with me are feeling the same way about it," Sopoaga added. "It's just an amazing feeling."
To be a starting running back in the NFL, you have to be supremely talented. So it should come as no surprise, the defensive unit respects every opponent it faces, especially the running back San Francisco faces this Sunday at Candlestick Park.
This time, it comes against St. Louis Rams star runner Steven Jackson, the last rusher to have a touchdown against the 49ers some 285 carries ago in a Week 16 victory which effectively eliminated the 49ers from the playoffs last season.
This time around, if the 49ers win, they'll be in the playoffs for the first time in nine seasons.
With much at stake, facing a top-caliber runner like Jackson is an added challenge to a 49ers defense which enjoys the physicality of such games.
"We have a solid defensive team, there are no prima donnas," Goldson added. "Everybody likes to get dirty. We have a secondary that loves to tackle. A lot of players at the corner position just want picks, but we have unselfish guys. That helps."
Now, those same unselfish players will look to take away the run like they've done for 33-straight contests and win a game that'll earn them the NFC West title.
"I've never been on a team that has a record like this, being able to win a title like this," Rogers said. "I've never experience it this early, too."
Rogers and rest of the 49ers defense won't let the clinching aspect affect their focus or preparation this week.
"This is a big moment for our head coach to come in and establish this and have his team ready with no offseason with a new system they were putting in," Rogers said. "It's a big game. Of course we want to clinch; you can't help but look at that. But if we continue to play ball like we usually do and it'll happen soon."