Led by a deep defensive line, the Bears had 21 sacks in the first six games and once ranked as high as No. 2 in sack percentage.
But they've dropped to 11th and have just 11 sacks in the last six games.
How important is the pass rush to the Bears' defensive success?
"It's everything," defensive coordinator Rod Marinelli said. "We say that all the time. We've got to stop the run because, if you don't get the run handled, you never get the rush off track. But (the pass rush) is something we've got to do."
Marinelli says it's nothing opponents are doing differently.
"It's usually about what we do," he said. "We've just got to get better."
Julius Peppers leads the team with 7 sacks, but just 2 have come in the past five games.
Henry Melton has 6 but just 1 in the last five games. Just 1½ of Israel Idonije's 5 sacks have come in the last six games, and just 1½ of Corey Wootton's 4½ sacks have come in the last seven games.
Shea McClellin has 3 sacks this season, but just 1 in the last nine games.
Rookie wide receiver Alshon Jeffery played just briefly in one of the past seven games, but he's probable Sunday after missing two games with a knee injury.
The struggling offense could use the skills the 6-foot-3, 216-pound Jeffery demonstrated in his first five NFL games, when he caught 14 passes for 184 yards before a broken hand shelved him for four games.
"We're excited to have him back," offensive coordinator Mike Tice said. "But I want to temper that because we haven't had him for any length of time this year to get him really in a groove."
With No. 2 receiver Earl Bennett (concussion) out Sunday, Jeffery would be a welcome secondary option after Brandon Marshall.
"Certainly he's shown in the games he's played that he can be a talent for us and certainly complement Brandon," Tice said.
"That really helps us because when they try to key on Brandon we really have two go-to guys on the field at the same time."
Kelvin Hayden has a lot in common with injured Tim Jennings, whose spot at cornerback he takes Sunday.
They were teammates for four years in Indianapolis. Both were second-round picks of the Indianapolis Colts.
Hayden, a Chicago native and Hubbard High School graduate, was taken 60th overall out of Illinois. Jennings was selected 68th overall a year later out of Georgia.
Hayden started 46 games and Jennings 21 in the Colts' Cover-2 defense.
But the 6-foot, 195-pound Hayden and the 5-8, 185-pound Jennings are different as players.
"They're out of the same system," defensive backs coach Jon Hoke said, "but they don't play similar. Obviously size has a little bit to do with that.
"They're both very knowledgeable players who play with good technique, and they're both tough guys. But the way they play is a little bit different.
"Kelvin's faster, and he's a bigger body. Tim's a quick guy, also with good speed, but they're different when you watch them play."