Mike Singletary as … a Linebacker
The first job of a linebacker is to stop the run. At the snap, they all take a read step toward the line of scrimmage. While they step, they watch the offensive linemen. If the offensive linemen block for a running play, then the read step gives the linebacker momentum to fill whatever gap opens up for the running back to come through. It's the linebacker's job to run wherever he has to go to stop the running back. That means watching the backfield to know who has the ball. It also means using his hands to keep offensive players from blocking him.
If the linemen set up to pass block, then the linebackers drop back into pass coverage. Most of the time, linebackers will be responsible for stopping receivers who run short routes across the field. Sometimes a linebacker will be assigned to watch the running back in case he comes out of the backfield to catch a pass. The specific coverage assignment depends on the team's defensive strategy. That strategy may well include linebacker blitzes, where a linebacker rushes the quarterback once he reads a pass play.
The linebackers serve key roles as communicators for the defense. Before the snap, the defensive linemen don't have a good view of the offensive formation because they are trying to get in a low-to-the-ground stance. The linebackers have to tell them what they see: which is the strong side of the offense, where there are more players? How many runners are in the backfield? Should the defense change its strategy? The linebackers will usually communicate this information using some sort of code words so the offense can't catch on.
Help from the Sideline
As soon as it's clear whether a play is a running or passing play, every player on the sideline yells “Run!” or “Pass!” On a passing play, as soon as the quarterback throws the ball, the sideline yells “Ball!” Linebackers and defensive backs make their own reads, but they can and do use the sideline's call to help them out.
Making the Tackle
More than anyone else on the defense, the linebackers are in charge of tackling. The defensive linemen try to force the running back to where the linebackers can make a tackle. A good linebacker is not only fast enough to get where he's supposed to be, but he's strong, too, with outstanding tackling form: head up, legs driving, arms wrapping the ballcarrier in a bear hug as he falls to the ground. Sure, all defensive players should be good tacklers, but the linebackers have to be the best.
A New Bear
Linebacker Brian Urlacher played four seasons for the University of New Mexico before the Bears made him their number one draft pick in 2000. He started at middle linebacker through most of his first year, and that's where he's stayed ever since. His success at that position, where he makes 10 to 15 tackles per game and covers the field like a monster, reminds fans of Chicago legend Mike Singletary.
Brian's strength (he set weightlifting records in college) allows him to take on and defeat the blocks of big offensive linemen. That makes it difficult to run on him. Brian's excellent speed allows him to cover the deep middle of the field. Because he is so good in coverage, the Bears safeties can focus on the receivers on the sides of the field, knowing that Brian has the middle taken care of. Brian played in the Super Bowl for the first time after the 2006 season, making ten tackles in a loss to the Colts.