In 2014, former Pittsburgh Steelers and Arizona Cardinals running back Rashard Mendenhall retired at age 26, walking away from millions in potential earnings. While Mendenhall may no longer be playing, he's still drawing on his NFL experience as a part of his new job.

Since retiring, Mendenhall, who made more than $13.8 million during his six-year career, joined the Writers Guild of America and worked as a writer on the first season of HBO's "Ballers," which aired its series premiere last Sunday.

"Ballers" is about an ex-NFL player who transitions to life as an agent. It stars Dwayne "The Rock" Johnson, and has been widely compared to "Entourage."

While a former NFL player seamlessly transitioning from football to screenwriting may come as a surprise, Mendenhall told USA Today's Lindsay H. Jones he knew this is what he always wanted to do once his career ended:

"I've always known I wanted to write. It was always a passion of mine — it was peace, a getaway. It was also, even while I was playing, it was kind of an artist mentality. You have a day job, but the art that you're working on is what you really want to do. ... I knew that when I was done playing, that's what I was going to do. It was kind of always a thing behind [football], I just didn't know what to what extent in television or see how it was going to shape up."

"The Rock" is an agent in Ballers. Gene Page/HBO/"Ballers"

Many athletes have a hard time transitioning to their new lives once their retire, but Mendenhall wrote a blog post for The Huffington Post saying that hasn't been the case for him:

"I wasn't supposed to walk away from the NFL, but I did. I wasn't supposed to be writing television, but I am. I'm supposed to be lost after football. I'm not. I've reinvented myself. This is my first transformation. I'm supposed to be broke right now, or maybe the statistics say five years from now. Either way, I'm not even close. I'm not supposed to be anything but a football player. But really, I'm just a guy who used to play football. There's a reason I'm doing this."

Mendenhall is a part of a trend of under-30 players retiring in their prime. Jake Locker, Chris Borland, Anthony Smith, Patrick Willis, Anthony Davis, and Jason Worilds all retired this offseason. Mendenhall told Jones he hopes to keep working on "Ballers" in the second season.