The reason is an injured hamstring, the type of thing that can linger for weeks. If you want to know more about what he's dealing with, you can check this excellent explanation by Dave Seibert.
This couldn't have possibly come at a worse time for Chicago.
The Bears are tied for the NFC North lead with the Green Bay Packers, but while both have 8-3 records, the Packers have a slight edge because they won the previous meeting in Week 2.
For now, the Bears reside in the first wild-card spot—fifth overall in the conference and one game ahead of the Seahawks, who now hold a tiebreaker over them. Hot on the heels of the Hawks are four teams at 6-6—Washington, Dallas, Tampa Bay and Minnesota.
Along with Minnesota, the Bears face the Packers again, as well as the Cardinals and Lions. While they should win at least two of those games, they have precious little margin for error. As we've talked about before, the loss of Urlacher isn't insurmountable, but it isn't going to be easy.
Urlacher's numbers aren't staggering this year, but his impact is really beyond numbers and won't easily be replaced.
When we were unsure what Urlacher's status was going to be back in preseason, we assumed Nick Roach would move to the middle linebacker position while Geno Hayes started strongside. That looks to be the case here, with some added depth from re-signing Dom DeCicco.
As said in August, I like Roach a lot, and his production will go up in the middle spot. The problem is that what Urlacher brings to the table—the experience to sniff out offensive adjustments, to call changes on the defensive side of the ball and to help fool offensive lines—isn't something which a part-time player like Roach can just "pick up."
Especially considering that Roach is moving inside from the outside slot—a very different skill set.
The upside is, Urlacher isn't exactly banned from the facilities, so he can be on hand to help Roach get up to speed on how to best approach each offense they face as the "mike" linebacker.
Still, you have to assume there will be some bumps in the road.
What this means is that someone else might have to step up to make adjustments on the defense, or at least assist Roach in doing so. More than likely, it will be Lance Briggs, another full-time snap guy who has been in the league long enough to have seen all the tricks.
Other players like Charles Tillman and Julius Peppers will likely add their voice as well. Ultimately, it takes a village to replace an Urlacher.
The other thing the Bears will have to overcome is making up for the huge amount of snaps Urlacher was on the field for.
Urlacher was on the field for 99 percent of the defensive snaps against Seattle, and the only reason it wasn't 100 percent was due to the injury. That's about average for Urlacher, and he had to be on point for all of those snaps and keep his energy level up.
Roach was on the field for just 45 percent of the defensive snaps. The difference in endurance between the two percentages is every bit as significant as the numbers make it look.
Against the Seahawks, the defensive unit looked gassed at the end of the game. Urlacher is a work horse, and even he was burned out by the end.
How many wins can the Bears get without Urlacher?
With everyone else having to pick up the slack in his absence, will the plan the Seahawks used—run at the defense until it collapses—be a blueprint on how to avoid letting this potent defense burn you?
In an effort to avoid putting rookie quarterback Russell Wilson in a position where he had to beat Tillman and Tim Jennings repeatedly, Seattle ran Marshawn Lynch.
The result was a defense which was on its heels in the fourth quarter and totally helpless to get a stop by overtime. We've got a similar situation with Minnesota this weekend—a quarterback who you don't want trying to beat the corners and a tremendous running back—so we'll see if they can repeat it.
With Urlacher gone from the middle of the field, running off-tackle (and in general) will look even more enticing. Roach and company will have to work extremely hard to contain teams looking to run.
The hope is that Urlacher can make it back for or during the playoffs. A hamstring injury can linger, so the Bears will want to rest him for as long as they can. The key is to make sure they don't miss the playoffs while they're letting him heal.
Luckily, the Bears defense is about more than the play of Urlacher, which is good, because the teams they play will give them all they can handle—especially Green Bay.
I'm on the fence about the Packers game without Urlacher. That's a toss-up to me in Soldier Field, though you can lean toward Chicago. Arizona has a defense which could be an issue, but the offense is so bad the Bears could field a team made of fans and win. And the Lions will play tough at home, especially if the Bears are on the precipice of missing the playoffs.
Detroit is going to be dangerous on offense, and while I would call that a win for Chicago, you just never know.
For me, the pivot game is this weekend against Minnesota. Sure, they beat the Vikings pretty handily a couple of weeks back, but that's really hard to replicate in a short amount of time. Going to the Metrodome complicates things further, and you can be sure that the Vikings will run Adrian Peterson at Urlacher's former spot.
It's going to be tough to stop Peterson (though, it may have been impossible even with Urlacher), but the defense will have to find a way to get Christian Ponder throwing since he has been picked off so often of late.
This was going to be a tough stretch even with Urlacher in the mix.
His absence means it will be that much tougher, and everyone needs to step up that much more if the Bears want to win the division, or even make the playoffs.
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