LINKEDINCOMMENTMORE

During a six-day stretch in March, the San Francisco 49ers saw the heart of their defense unexpectedly vanish.

Patrick Willis was the first player to leave. The five-time All-Pro linebacker and seven-time Pro Bowler retired after toe surgery forced him to miss 10 games last fall. He was 30, with perhaps half a career ahead of him.

There was no replacing Willis’ credentials, but what happened less than one week later was an even more shocking blow. Chris Borland, a third-round draft pick last year, stunned the NFL when he announced his retirement over concerns about the long-term effects from concussions. The former Wisconsin linebacker was a budding star, Willis’ apparent heir.

They weren't the only lowlights of a tumultuous offseason in San Francisco. Defensive tackle Justin Smith retired in May, and defensive end Aldon Smith was released in August after multiple off-field issues.

“We’ve got a good group of people here,” 49ers coach Jim Tomsula said this week, “and there’s a good core of people, and building around that. The strength is always in the people. We all know that. I think we have that and we’ve got to continue.”

In his next breath, Tomsula admitted his team is a “work in progress.” The team that went to three straight NFC title games from 2011-13 is just 1-2 this season. While it’s been a tumultuous year for the entire organization, no area has suffered more than the 49ers’ defense.

The Opposite Sideline: 49ers reeling
Packers confident against Kaepernick

The 49ers ranked among the league’s top five defenses in fewest yards allowed over the past four seasons. They ranked top five in fewest points allowed for three straight years before finishing 10th last season. This season, the 49ers rank 25th with 382.3 yards and 31st with 31 points allowed per game.

While 49ers quarterback Colin Kaepernick has given the Packers’ defense problems, San Francisco’s defense also has been problematic at times for the Packers’ offense. During a four-game losing streak against the 49ers that started in 2012, the Packers hit the 28-point mark twice. They were held to 22 points in 2012 and 20 points in a home playoff loss two seasons ago.

The Packers were outrushed in all four games. In their two lower-scoring losses, they averaged 54 rushing yards per game. When the Packers play at the 49ers on Sunday, they’ll see a very different defensive unit.

“I mean, the guys that came in to replace definitely aren’t the guys who were there before, which helps us out a little bit,” Packers running back Eddie Lacy said. “But it doesn’t make the game any easier. We still have to go in there with the same mindset — the same, physical mindset. Even though it’s an away game, we want to go in there and dominate.”

After a 20-3 home win against the Minnesota Vikings in the opener, the 49ers allowed 43 points at Pittsburgh and 47 points at Arizona the past two weeks. Still, Lacy said, their defense has enough pieces remaining to be effective, especially at home.

It remains to be seen how linebacker NaVorro Bowman will play throughout the course of a season after missing 13 games with an ACL injury last year, but the three-time All-Pro has been an elite player in the past. Safety Antoine Bethea, a Pro Bowler last season, is also a new addition since the last time the Packers met the 49ers. Lacy said the 49ers defensive front is also effective, even without Justin and Aldon Smith.

“They two-gap a lot,” Lacy said, “so they come off blocks good. As far as the running backs go, we just have to press our landmarks and try to get them to stretch or get them to come in and go around. So it’ll be a lot of little mind games going on out there, but they do good up front.

“They get to the ball. If you break one tackle or get past one guy, there’s going to be two or three more guys there. It’s all about being physical so when those other guys do come, we’re going to give them contact before they give it to us so we can continue to get those extra yards.”

rwood@gannett.com and follow him on Twitter @ByRyanWood

LINKEDINCOMMENTMORE