"As a kid, it was my dream to play in the NFL. I played my first full season of tackle football in second grade," Castonzo said in a statement. "Now I have played my last. As I sit here now, after a 10 year NFL career, I am extremely proud of all the hard work and sacrifice that allowed me to evolve that dream into a goal, and ultimately into a reality unlike anything I could have even imagined."
Castonzo, a first-round pick in the 2011 draft, started all 144 games he played in his career. The Colts were 4-13 in the games he missed in his career.
"If you would have had told me after [rookie] training camp that I would have a 10-year career, I would have laughed in your face," Castonzo said during a video news conference with reporters.
He said his decision to retire is final.
"I made the decision. I'm sticking to it," he said.
Castonzo flirted with retirement after the 2019 season but decided to put it off. He signed a two-year contract with the Colts in the winter of 2020, but he said at the time that he planned to take his playing status on a year-by-year basis.
Injuries took a toll on Castonzo this past season. He missed four games because of a knee and ankle injury. The Colts announced on Dec. 30 that Castonzo would miss the rest of the regular season and then their playoff game against Buffalo, which they lost, because of ankle surgery.
He said Monday, however, that his injuries this season did not play a part in his decision to retire.
"The Colts have been blessed with many talented offensive linemen throughout our rich history and Anthony Castonzo is among the best to represent the Horseshoe," Colts owner Jim Irsay said in a statement. "For 10 seasons, Anthony consistently handled premier pass rushers at one of the toughest positions to play. He quickly developed into the leader of our offensive line and set a standard for preparation, strength and conditioning, and play. Anthony deserves a tremendous amount of credit for helping our offensive line mature into one of the best units in the NFL. He will sorely be missed, but we are so appreciative of AC's contribution to our organization and we congratulate him on a fantastic career."
The Colts might look inside the organization to find their replacement at left tackle for Castonzo. Coach Frank Reich said guard Quenton Nelson, who has been an All-Pro at that position in all three years he's been in the NFL, is a possibility. Nelson, who had never played left tackle in his NFL career, played a few snaps there against the Las Vegas Raiders on Dec. 13.
"[Nelson] as an option out there is certainly a realistic option that -- [GM Chris Ballard] and I have already had that conversation obviously when AC got hurt," Reich said earlier this week. "It was like, 'Hey, well, let's take a look at Quenton, maybe that's a real option.' I'll let Chris go into more of the detail on that when he gets with [the media] on Thursday. But yeah, that would certainly be an option, but like every other decision, you have to look at all options and consider all factors."
Castonzo said he talks with former Colts quarterback Andrew Luck, who retired before the 2019 season, regularly when asked Monday what it will be like with his playing career over.
"We're still good friends. I asked him, 'What's it like?' But I definitely leaned on him, because he's been through it," he said.