By Adam Hoge-

LAKE FOREST, Ill. — Here’s everything you need to know on a defensive-centric day at Halas Hall:

1. The 49ers’ rushing attack is probably the toughest the Bears will see all season. It’s a common claim you hear around the NFL: San Francisco runs the most impressive running scheme in the league.

Part of the reason why it is so hard to prepare for is because of how many different looks the 49ers give you: pistol, zone-read, zone-blocking, man-blocking, traps, e.t.c.

“They’re really sharp and they’re very efficient in where guys align, their motions,” Bears linebacker Lance Briggs said. “They take advantage of whether we want to call where there’s going to be one back or two back.”

That call is something the Bears got beat on in overtime against the Bills, when Buffalo shifted the tight end into a two-back set. Briggs made the check to a “two-back” set, but safety Ryan Mundy missed the call and trailed the tight end back across the formation at the snap, instead of staying in the “B-gap” as was assigned after the check. 38-yards later, Fred Jackson had the Bills lining up for the game-winning field goal.

Cleaning up issues like that will be the focus this week after the Bears allowed 193 rushing yards to the Buffalo Bills last week.

“They are going to line up and they will run the power down your throat,” Bears defensive end Jared Allen said. “So they are still a conventional run team. We look at that team and it’s power, it’s lead and it’s counter, and they’re going to run the ball down your throat. But you’re going to get it with different window dressings.”

One of those window dressings is something the Bears call “wham”, a trapping technique where an offensive lineman lets the defensive lineman go by him, trapping him into the fullback or tight end, which opens up the gap. The offensive lineman then gets to the second level, blocking a linebacker.

“They’ll ‘wham’ just about everybody on the defense and force a different player on the defense to be disciplined and make sure he’s in that gap,” Briggs said. “If he gets pushed by, it creates another alley for Frank Gore and Carlos Hyde to run.”

To counter, the Bears will have to rely on their new “one-and-a-half gap” scheme, which is designed to keep blockers off the linebackers. The scheme appeared to be sound in the opener against the Bills, as the issue on the big runs was a lack of execution by the players.

2. Speaking of a lack of execution, the players have not been afraid to own up to their mistakes. Briggs was guilty of being out of his gap on Anthony Dixon’s 47-yard run and cornerback Tim Jennings told 87.7 The Game Tuesday that Briggs immediately went back to the huddle and took responsibility for it, which allowed the rest of the defense to move on to the next play.

3. Defensive coordinator Mel Tucker claims that specific play wasn’t a zone-read. 

Asked about the struggles against the zone-read Wednesday, Tucker said: “It wasn’t necessarily zone-read plays, there were a couple runs that hit. (The Bills) average about 12 zone-read plays a game and we got about 12 in the game and they were about three yards per carry on those plays. The couple plays they hit were just basic zoner plays, not reads, and so we need to play those better.”

But that doesn’t seem to jive with what the film shows on Dixon’s 47-yard run or with what Tucker’s players are saying.

“I saw the read-option,” Briggs said about the play. “We were in an eight-man front. I should have just stayed in my gap. I popped out to go get the quarterback, and left that gap wide open. That’s a mistake that I don’t normally make. And I won’t moving forward.”

When you look at the film, EJ Manuel appears to “read” safety Ryan Mundy and hand the ball off to Dixon because Mundy is in place to stop Manuel if he keeps the ball. It’s possible it was a straight give the whole way, but even if that was the case, it acted as a zone-read, which got Briggs out of his gap. Thus, it’s misleading for Tucker to claim “it wasn’t necessarily zone-read plays” that were the problem.

4. Briggs is leaning on experience to avoid hitting the panic button. He knows Sunday was not his best game, but he’s been there before.

“I told Mel yesterday on my day off, I’m like, ‘Man, you know, I once came out in our first game and had 36 loafs and one tackle against Atlanta, and got some of the same criticism; went on to have a regular year.’ I’m not like everybody else,” Briggs said. “I don’t hit the panic button. For us, it’s time for us to focus on beating the 49ers.”

That game against the Falcons was three years ago, the last time he was a Pro Bowler.

5. Jared Allen is not worried about his age. The 32-year-old defensive end did not have a great debut with the Bears Sunday, but he claims it’s not because he’s slowing down.

“I feel like I’m 18,” Allen said. “Honestly, I feel better this year than I did last year. Body feels great, strong. I lifted this morning. Weights are going up. I kind of judge everything off how my workouts go because my workouts are the same in-season. So I feel phenomenal. I watched film. I’m more explosive than I was last year as far as like first-step explosiveness.”

Allen signed a three-year deal with the Bears in the offseason and doesn’t appear to be ready to retire anytime soon.

“We come in and say, ‘We’ve got to do X, Y, and Z to get ready.’ And the day I can’t do X, Y and Z to get ready, trust me when I tell you, I will be the first one to leave because I’m not going to sit up here and be the reason why my team loses,” he said.

6. In Allen’s defense, it’s harder to rush the passer against mobile quarterbacks. When you’re constantly worried about run-fits and keeping a quarterback contained to the pocket, it’s harder to get up field.

“It’s block-reaction and the difference between guys that make plays and guys that don’t is how fast you recognize the block-reaction and how fast you read what your key is giving you,” Allen said.

The defensive end added that there are really only four blocks he has to worry about.

“I always tell people that football’s not that hard. As a d-lineman I get four blocks: I’m going to get a cut-off, a reach, a base block or a pass to tell me where the ball’s going and if I can stay true to my keys, we can be successful.”

7. Those keys will be tested even more against Colin Kaepernick, who torched the Bears two years ago. That was his first start in the NFL and the 49ers beat the Bears 32-7 at Candlestick Park on Monday Night Football.

Asked Wednesday what he remembered about that game, Briggs said: “I remember, ‘Touchdown. San Francisco. Touchdown.’”

Allen, who conducted his press conference at the same time as Briggs, quickly interjected: “I remember that too!”

8. The Bears’ injury report is busy. It’s only Week 2, but there are plenty of names to keep an eye on this week.

Players who did not practice Wednesday include: Wide receiver Brandon Marshall (ankle), wide receiver Alshon Jeffery (hamstring), center Roberto Garza (ankle), left guard Matt Slauson (ankle), fullback Tony Fiammetta (hamstring) and third-string quarterback David Fales (shoulder).

Marshall is expected to play Sunday, but Jeffery is more of a question mark. At this point, it seems doubtful Garza or Slauson will be ready.

Meanwhile, wide receiver Josh Morgan (groin) and cornerback Charles Tillman (coaches’ decision) were limited Wednesday.

The wide receiver position is one to watch. With only four receivers on the 53-man roster and three of them on the injury report, Josh Bellamy may need to be elevated from the practice squad before Sunday’s game.

9. Jim Harbaugh is a stressed out man on a game day. The 49ers’ head coach joined Chicago reporters on a conference call Wednesday and said:

“Every NFL game I go into, the night before the game, I sleep like a baby — I wake up every hour crying. And during the game, I feel like I’m sitting in a dentist chair getting a root canal done on me for three and half hours.”

10. According to a league source, referee Carl Cheffers has been assigned to Sunday night’s game between the Bears and 49ers.

 Adam Hoge covers the Bears for 87.7 The Game and TheGameChicago.com. Follow him on Twitter at @AdamHoge.