Last line of defense failing

There is no denying the Chicago Bears are a rattled team.

Their right-handed quarterback resorted to throwing lefty last game. Their offensive linemen are lucky if they recognize who's lined up next to them from week to week.

But the most resounding evidence that they have been shaken to their very foundation is that their very foundation is shaken. The same defense that has kept the team afloat in recent years, a defense that could always stop the run and prided itself on largely avoiding the big play, has been more vulnerable than a spurned lover.

They're even talking about trust issues.

And in the biggest indication yet that coach Lovie Smith recognizes the severity of the problem, veteran safeties Chris Harris and Brandon Meriweather have both been benched for this Sunday night's game against the Minnesota Vikings, to be replaced by Major Wright and rookie Chris Conte.

"Sometimes, it creates a sense of urgency," said defensive coordinator Rod Marinelli, not confirming the changes but certainly conveying the mood.

But the problems are spread throughout the defense.

Ranked 29th in the league in total defense, the Bears are 28th in rushing yards allowed with 135.6 per game. They are tied with Carolina, New Orleans and Philadelphia for worst in the league with three runs of 40 or more yards and are sixth-worst with five runs of 20 yards or longer.

They have given up six passes of 30 or more yards.

Last year at this time, the Bears were ranked sixth in total defense and fourth in rushing yards allowed with 78.6 per game. And for the season, they gave up just one run of 40 or more yards and 13 of 20 or more. In 16 games, they allowed nine passes of 30 or more yards.

While Lance Briggs appeared to be in denial Thursday -- "Watching film, we did a lot of good things," he said of the Monday Night drubbing by Detroit. "A lot of good things." -- Brian Urlacher was refreshingly honest.

"The mental errors and mistakes are killing us right now," he said. "They are fixable, which is a good thing for us, but we just have to do it. It's been five weeks now and every game, we just keep getting gashed. We have to stop doing it."

Against the Lions, the Bears were victimized for 181 yards on the ground and had two passes and two runs (both by Jahvid Best) go for 88, 73, 58 and 27 yards. Three more Matthew Stafford passes went for 18, 17 and 15 yards and another run by Best went for 15.

When Biggs speaks of defending the run well "most of the game," it's the old "So other than that, Mrs. Lincoln, how was the play?" A team can give up any number of 3-yard runs, but if their opponent sprinkles in enough 12- and 15-yarders, not to mention an 88- and 58-yarder, it's a bad defensive performance.

"It hasn't happened around here in a long time, big plays like that," Urlacher said.

So what exactly is the problem?

On the big running plays, Bears players say it is all about discipline, the old gap control problem. And Urlacher said it just keeps feeding on itself.

"Now it's getting to the point where, when you run to your gap and you're getting headsy, looking around to see where the ballcarrier is and he cuts back in your gap," he said. "It's a trust issue with us and being disciplined and trusting other guys are going to be in their gap. That's what it comes down to right now for us."

That, and missed tackles, which is especially troubling with Adrian Peterson coming to town this Sunday.

"Usually when something pops in the run, either it's a missed tackle or someone in the front seven or eight not in their gap correctly," defensive coordinator Rod Marinelli said. "It looks horrible when we don't get in their gap correctly."

Defensive tackle has been a disaster this season. But with nose tackle Matt Toeaina (who replaced the injured Anthony Adams) now out with a knee injury, we should finally get a look at second-round draft pick Stephen Paea in his first regular-season appearance this Sunday night against Minnesota.

"He definitely has a chance to see some time this week," Marinelli said.

Almost overlooked with all of their other difficulties is the Bears' relative lack of takeaways (eight leading to 28 points), which goes to a general shortage of defensive intensity this season. Last year through five games, they had 14 leading to 21 points.

Players become defensive when asked about the Cover-2, which is designed to avoid the long pass play, repeating the standard line that everyone plays some Cover-2 in passing situations.

"We play 15, 18, 20 percent of it," Marinelli said. "We play a lot of other stuff with it. With us, it's more about how we do things. It's a system of doing things correctly."

He's right, of course.

Melissa Isaacson is a columnist for ESPNChicago.com.