The Steelers cut him two days before Christmas and he signed with the New England Patriots to finish the season, helping them advance to the Super Bowl. However, he has chose to leave football in the rearview.
This isn't the first time Harrison has hung up his cleats, but it's likely to have more finality than his initial flirtation with retirement. "Many thanks to my family, coaches, the fans, and everyone who played a role in my football life", he wrote on Instagram.
Harrison played almost his entire career with the Steelers and the 84.5 sacks he collected while wearing black-and-gold are a franchise record. He retired briefly in September 2014 only to be lured back to the Steelers.
This is the second time Harrison has called it quits.
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During media availability at Super Bowl LII, Harrison said he was planning to return in 2018.
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The Steelers released him late in the season to make room for offensive tackle Marcus Gilbert, who was being activated from a suspension.
Earlier this month, ESPN's Jeremy Fowler reported that Harrison meant to play in 2018 and hoped to sign with someone as a free agent after this month's draft, but apparently he's had a change of heart. The Ravens were reportedly interested in Harrison, but he signed with the Patriots, causing an uproar in Pittsburgh.