Posted by ESPN.com's Kevin Seifert
The quick answer, of course, is quarterback Jay Cutler.
Wednesday, ESPN.com is identifying veterans on the hot seat throughout the NFL, and you would think most NFC North eyes will be focused squarely on the Bears' new quarterback. But if you scour the Bears' roster, you'll find a player with at least the same potential to impact the Bears' season. Defensive tackle Tommie Harris is only one year removed from an eight-sack season and could personally return the Bears to defensive prominence if he can reestablish himself as a premier interior pass-rusher.
The Bears' scheme is largely predicated on consistent pressure and penetration from defensive linemen, and Harris is best equipped to provide it. Coach Lovie Smith hired one of the NFL's top defensive line coaches to help him in Rod Marinelli, and the Bears' decision not to address the position in free agency indicates they are counting on Harris to pick up where he left off in 2007.
Without a reliable pass rush, the Bears might be compelled to continue the heavy blitz packages that largely got them into trouble last season. Devoting linebackers and safeties to the pass rush leaves the rest of the defense exposed, especially when defensive backs are put in one-on-one coverage situations. You hate to put too much pressure on one player, but the old Tommie Harris could allow the Bears to return their scheme to a four-man rush.
If you want to know the limitations of a Pro Bowl quarterback on team with a sub-par defense, check out Denver's record last season with Cutler at the helm.
Honorable mention: Green Bay left tackle Chad Clifton. The Packers already have a significant hole on the right side of their line, where injured incumbent Mark Tauscher (who is also a free agent) might not be ready to play when the season begins. Clifton, who turns 33 next month, seemed on his last legs at times in 2008 and had surgery on both knees after the season. The Packers need to squeeze at least one more year out of him to avoid a one-year overhaul of their offensive line.