The cover-2 defensive scheme became the signature defense of the Chicago Bears under coach Lovie Smith, and with his firing Monday it could signify the end of careers as well as an era in team history.
It's possible the Bears could bring in a head coach who prefers the 3-4, which would run contrary to the franchise's long middle linebacker tradition that started with Bill George, Dick Butkus, Mike Singletary, and now Brian Urlacher.
If it happens, Urlacher and other defensive players could be out. Urlacher could be gone, anyway, since he finished the season watching from the sideline with a bad hamstring and is without a contract for 2013.
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Urlacher wasn't available at Halas Hall Monday to talk about his future, but Sunday night told Fox television in Chicago that he doesn't plan to retire.
"I still feel like I can play some football," he said. "An offseason of rehab will help and whatever happens, happens. If it's not here, then it won't be here."
Urlacher is experiencing something new.
"Yeah, I'm a free agent right now," he said. "I guess, I don't know, I've never been in this situation before, so I don't know how that works."
Urlacher isn't the only defensive free agent who could be affected by the change. Pro Bowl DT Henry Melton is a three-technique DT, a position unique to Smith's system. He's also an unrestricted free agent, so whether he would even be wanted in a new defensive scheme is up to the new staff. Linebacker Nick Roach is a free agent, as is DE Israel Idonije.
The scheme will make a big difference in terms of future personnel on defense. Three-man defensive fronts are usually two-gap systems with bigger defensive linemen needed to occupy blockers while linebackers make the tackles. The Bears scheme is different because the defensive linemen are smaller, lighter and attack upfield in gaps. So they may have to overhaul the entire D-line.
"We could have a similar defense," DE Corey Wootton said. "There's a lot of Tampa-2 schemes out there (like Smith runs). So who knows? We could have a 3-4. You never know. It's kind of up in the air."
It will make for an interesting transition.
"There will always be a transition when you do a different type of defensive style," Wootton said. "Here up front now we're used to attacking, so it could be all different. We don't know."
As bad as the Bears offense was under Smith, it would be difficult to envision a Bears defense in the future that can force 44 turnovers and score eight TDs like this year's group. Smith's defenses had 310 takeaways during his nine seasons, the highest number in the league during that time period. They forced more fumbles, had the best third-down percentage, and forced more three-and-outs than any other defense, while holding offenses to the lowest red zone TD percentage.
How this changes with a new head coach is any defensive player's guess.
"I've never gone through a coaching change, so I'm not sure," Roach said. "I don't know how typically the head coach will influence whatever his side of the ball was, the change for that. So we'll have to wait and see."
Follow Bears reporter Gene Chamberlain on Twitter @CBSBears.