Determined to improve a Bears defense that ranks last in the NFL against the run, coordinator Mel Tucker is continuing to emphasize run fits and gap integrity in practice and meetings.

"In order to play great defense, especially run defense, everyone needs to be exactly where they need to be on every play," Tucker said. "It only takes one breakdown to cause a big play. We really don't have margin for error, especially when you're playing good teams with good talent."

Khaseem Greene (59) and Christian Tupou (64) are among a handful of rookies playing on defense.

The Bears have allowed an average of 197 yards rushing in their last five games and face reigning NFL MVP Adrian Peterson Sunday in Minnesota. The Vikings star ranks second in the league in rushing with 997 yards and 10 touchdowns on 226 carries.

Last Sunday, Rams rookies Benny Cunningham, Zac Stacy and Tavon Austin combined to rush for 261 yards and three touchdowns in a 42-21 victory over the Bears.

"Everything we saw [on tape] was correctable," Tucker said. "A lot of it we were able to correct in the game. The biggest thing for us is just taking it from the practice field to the game. That's huge."

Having lost Charles Tillman, Lance Briggs, Henry Melton, D.J. Williams and Nate Collins to injuries, the Bears have had to utilize several young inexperienced players on defense.

"We've got to go back to work and get our guys who are getting on-the-job training to do a better job of focusing in on their keys and not getting caught up in all the other things that go on," said coach Marc Trestman. "And then the guys who have been around not getting so caught up in trying to help the guys who are in their on-the-job training and just focus on their work."

Despite the defense's lack of success this season, Trestman still has faith in the unit.

"There's evidence there that we can get the job done, and that's the way we're starting the week," he said. "That's what we as coaches are trying to do is to continue to work at that and put ourselves in a better position to make those stops. We know we can't make all of them, but to minimize No. 1 the explosive plays and No. 2 to begin to create some turnovers, which we haven't done the last couple weeks."

Trestman conceded that it's difficult to get young players to focus solely on their responsibilities. In recent weeks, the Bears have played five rookies on defense: Linebackers Jon Bostic and Khaseem Greene, and linemen David Bass, Christian Tupou and Cornelius Washington.

"It's not easy," Trestman said. "That's part of raising young players to be the players you want them to be. What we're trying to convince them to do is not worry about anybody else because they're probably not at a stage where they see the big picture because that takes time.

"So just learning what they do in the framework of their telephone booth and just focusing in with blinders on their specific key that's going to take them to the right spot. And then as I said the flipside of that is the veteran player who has a big picture and also knows that this guy is going to need some help and then he goes outside the parameters of his job. That's the discipline that we're trying to work on.

"There have been moments over the last three or four weeks that we've had that and there have been moments certainly as we all know that we haven't. That's the challenge week-to-week."