Colts' Anthony Castonzo plans for future by learning to create video game

Costanzo's life off the field as a coder (3:24)

Colts' left tackle Anthony Costanzo shares his experience as a coding extern when he's not on the football field. (3:24)

INDIANAPOLIS -- Indianapolis Colts left tackle Anthony Castonzo is in the prime of his NFL career. He's started all 89 games that he's appeared in during his six-year NFL career. He's headed into just the second year of his four-year, $43 million contract extension.

But Castonzo, 28, isn't thinking about just today. He's already looking ahead to his future.

He went through a three-week externship with Whalerock Industries, a technology company based in Southern California, earlier this offseason.

"I was looking through the list of externships that the NFLPA offers and it had a lot of different marketing and practical stuff, and then I saw one that was computer coding," Castonzo said. "I thought it would be fun and something I would be interested in, so I gave it a shot. I was gaining experience in a field that seems like something I would be interested in after football. If I didn't take advantage of the opportunity this year who knows if it would be there down the road."

The NFL Players Association has spent the past four years selecting players to do externships during the offseason at different companies around the country so they can prepare for life after football.

Castonzo chose computer coding because it allowed him to combine two things he enjoys other than protecting quarterback Andrew Luck's blindside: math and video games.

"I've always liked technology, but I never really studied it," Castonzo said. "I've always been impressed with what computers could do just because it's fascinating. They take nothing and make it into something based on codes. It blew my mind away."

Despite being known as the starting left tackle for the Colts, Castonzo was not given any special treatment. He was known as a guy with an interest in learning how to become a game programmer.

He sat his 6-foot-7, 311-pound frame down at his work station surrounded by the rest of his co-workers. He had bosses to answer to and worked from 9:30 a.m. to 5:30 p.m. Monday through Friday.

Castonzo was so worried about messing up that he spent his first week on the job at his station while watching other people roam freely throughout the office.

"It was kind of like I got transported back to rookie year coming into something," he said. "Even in my rookie year I knew something about what I was doing. This was very different. I had no idea on this. They definitely took a teacher-student approach with me, which was awesome. They did an unbelievable job making sure I knew all the basics. Building me from the ground up."

Castonzo was able to start building his first game, "Defend Your Kingdom," after learning programming languages such as Swift, CSS, Python, HTML and React. He kept the game, which is on an iOS app, simple. It consists of a few fighting characters that each have a handful of moves.

"They each only had two or three moves and on the third move you got was like a supercharge move," Castonzo said. "I kept things pretty basic and balanced out what each character could do. I didn't want anybody more overpowering than the other person."

Castonzo couldn't put his NFL job to the side during those three weeks. He made the five-minute walk from the office in West Hollywood, California, to his residence after work to grab a sandwich before going to work out. Colts strength and conditioning coach Darren Krein set up a trainer for Castonzo while he was there. After working out, he ate dinner around 9 p.m. and then spent a couple more hours programming codes before bed.

"I had a blast with developing things with apps and web design," he said. "I've always loved math, loved the problem solving. Everything has an answer eventually if you can think hard enough. It's very similar in terms of coding, thinking of different ways to do the same thing. It's a constant challenge, which really spoke to me.

"I came out of it thinking it was awesome and knowing I want to continue doing it."