The Pittsburgh Steelers have ranked in the Top 10 in total defense in each of the last ten seasons, including No. 1 overall in 2004, 2007, 2008 and 2011.
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A unit performing at such a high level year in and year out is a challenge as players are lost to free agency and retirement, but the Steelers have done an outstanding job of drafting and developing players at positions where turnover will take place in a season or two.
The Steelers lost a few key veterans, including some to retirement, this offseason. Appearing on NFL Network's "NFL AM" on Tuesday, Keisel told Eric Davis that he doesn't think there will be a drop in performance.
"I think we're going to be good," Keisel said. "We've got a lot of young guys stepping in and filling for guys that were legendary Steelers in Aaron Smith, and James Farrior and Chris Hoke on defense. So there are a lot of opportunities there for these young kids and I expect us to be tough like always."
Hood and Heyward will be competing for Smith's starting job this summer, with the other filling Hoke's role as a key reserve. That won't be the only change on the line as Steve McLendon and Alameda Ta'amu may be called upon to fill in at nose tackle for Casey Hampton, who is on the physically unable to perform list after tearing his anterior cruciate ligament in January.