At the end of the season, he entered free agency.
He finished off the post with the hashtag #2ndAndFinalRetirement.
Harrison finishes his career with 84.5 sacks, 34 forced fumbles and eight interceptions to go along with 795 total tackles. He made the Pro Bowl five times and was named an All-Pro twice during his 15-year National Football League tenure.
Despite an illustrious career with the revered Pittsburgh Steelers, Harrison and the team parted on negative terms.
He then spent some time with the Baltimore Ravens and the NFL Europe's Rhein Fire before ending up back with the Steelers in 2004. He remained productive into his late 30s, registering at least five sacks from 2014-16.
Harrison was undrafted out of Kent State in 2002.
Harrison, who turns 40 next month, posted a collage of pictures of his two sons and noted he's "missed way too much for way too long. and I'm done". He returned to Pittsburgh after injuries decimated the team's linebacker group and in his second act became a valuable leader on the field and elsewhere, often including teammates in his draining (and well-documented) offseason workout regiments in Arizona. However, he had a change of heart and continued to play on for a few more seasons. Harrison indicated during the playoffs he thought he had another year in him, but it appears he's changed his mind. Pittsburgh cut him on December 23, 2017, after he had played in only five games and been a health scratch much of the season.