Harrison, 39, wrote a lengthy Instagram post Friday, detailing his departure from the Steelers. The 6-foot, 242-pound defender joined the franchise as an undrafted free agent in 2002.
He went on to win two Super Bowls during his 14-year tenure with the team. He was also named an All-Pro twice and made the Pro Bowl every year from 2007 through 2011.
The Steelers' franchise leader in sacks was released on Saturday. He signed with the New England Patriots after clearing waivers.
After his release, Steelers players made some pointed comments about their former teammate. Center Maurkice Pouncey wanted to set the record straight that it was Harrison who wanted out of Pittsburgh.
"If anybody thought I signed a two-year deal with a team in the NFL at age 39 to sit on the bench and collect a check and a participation trophy, they're mistaken," Harrison wrote on Instagram. "I didn't sign up to sit on the bench and be a cheerleader. I was clear about that when I signed, and I was told I would be on the field when I signed. When I was asking for reps in camp, I got none. I got lip service though: we know what you can do - you don't need the reps. But I know what my body needs in order to be in shape to compete, and I said so, but still zero reps.
"At the beginning of the season, when it was clear I didn't have a role anymore, I asked to be released. Throughout the season, I was told week in and out that I'd be used. I wasn't. I started getting frustrated about the whole thing. I asked to not be dressed or take unnecessary practice reps if I wasn't going to play. That's what happened for a [couple] weeks, then we had a game week that I got solid reps in practice and everyone assumed I would play. I got to the stadium four hours early as usual, and my locker was empty. Nobody said anything to me about being inactive, just an empty locker. I asked to be released again. I was told no.
"A couple weeks later, they dress me for the game so I assume I'm going to play, and I get zero reps. Stood on the sideline the whole game. I asked to be released again, I was told no. Then a few days later, they released me. I was never told I would be brought back, it was: If I bring u back, be in shape. I cleared waivers, and they didn't call. New England called. Also, to be clear, ask Ryan [Shazier] if I came to see him in the hospital. I didn't help Bud [Dupree] or TJ [Watt]? Ask TJ if I helped him.
"Maybe I didn't handle my frustration the best that I could've. If you haven't learned anything about me over the last 16 years, I'm a competitor to my core. I live and breathe competition. I do what it takes to keep my body and my mind ready to be on that field. I do it for me, I do it for my family, I do it for my team and I do it for the fans. Nothing else to it. At the end of the day, they made a business decision and so did I."
The Steelers face the Cleveland Browns at 1 p.m. Sunday at Heinz Field. The New York Jets face the Patriots at 1 p.m. Sunday at Gillette Stadium in Foxborough, Mass. Harrison is listed as a third-string linebacker on the Patriots' unofficial depth chart.