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The Pittsburgh Steelers now know of at least one significant change they will face in the offseason.
Defensive coordinator Keith Butler informed the team that he is retiring, the Steelers announced Saturday.
"It is an emotional day as I announce I am retiring from my football coaching career," Butler said in a statement. "I have spent every year since 1990 as a coach in the NFL and the NCAA, but the time is right for me to walk away after a successful career both playing and coaching the game I love.
"I want to thank the Rooney Family, Bill Cowher, Mike Tomlin and all the coaches and players that I have been involved with over my entire coaching career. I look forward to spending more time with my family, whom have been so supportive of me throughout the years. I wish nothing but the best to the Pittsburgh Steelers, and I will be cheering them on during my retirement."
Butler, 65, has served as Pittsburgh's defensive coordinator since 2015. He previously served as linebackers coach from 2003-14, helping the team win two Super Bowls during that span.
From 2017-20, Butler's defenses ranked in the top six in yards allowed. This season, outside linebacker T.J. Watt tied the NFL's single-season sack record, making him the front-runner to win Defensive Player of the Year.
Butler was a second-round pick of the Seattle Seahawks in 1978 and went on to play 10 years as a linebacker for the franchise.
The Steelers are expected to undergo several more changes this offseason, including the likely retirement of longtime starting quarterback Ben Roethlisberger. Cornerback Joe Haden and wide receiver JuJu Smith-Schuster are among the team's notable impending free agents.
Follow USA TODAY Sports' Michael Middlehurst-Schwartz on Twitter @MikeMSchwartz.
This article originally appeared on USA TODAY: Steelers' Keith Butler retires after lengthy NFL coaching career