(TNS) — Don’t try to ask Sebastian Castro about his defensive prospects. Don’t pick his brain on playing safety versus nickelback, or where he might sit on the depth chart now that Minkah Fitzpatrick has gone back to the future in a DeLorean fit for Biscayne Boulevard.

“The defense? I gotta get on special teams first,” Castro said. “That’s where I’m gonna earn my spot, really.”

If nothing else, Castro can deal with humble beginnings. Growing up in the South Side of Chicago suburbs, Castro lived in his grandparents’ house, sharing a room with his mother and older brother through high school.

Six years later, he’s taking a crack at cracking the Steelers roster as an undrafted free agent out of Iowa. He’s as logical a pick as any for this year’s training camp darling, an underdog who becomes a fan favorite for making plays and trying to defy the long odds against him.

Castro, who turns 25 in October, is a little old for a rookie. He’s a little slow for an NFL defensive back. And yeah, he’s a little smaller than you’d like for a safety at 5-foot-11, 203 pounds. But he had four interceptions, five forced fumbles, two sacks and 14 pass breakups over the three seasons he started for the Hawkeyes, so he’s no stranger to finding the ball.

Those are the back-of-the-trading-card facts. There’s more to Castro, though, that could make him a folk hero if all goes well. He throws his body around with reckless abandon, which makes sense. Two players he modeled his game after growing up were his older brother Roque, who also played safety in college, and another familiar face at that position …

“Oh yeah, Troy Polamalu — all the time,” Castro said. “I tried to play like him when I was younger.”

Castro also proudly represents his Mexican heritage, and the Steelers are perhaps the most popular NFL team south of the border. A third-team All-Big Ten selection, he was one of a few players of Mexican descent in this year’s draft, but the only one to end up in Pittsburgh.

Longtime Iowa coach Kirk Ferentz, an Upper St. Clair native, recalls Castro “really came out of his shell” before the team’s bowl game a couple years ago. Still, he’s more Polamalu than Ryan Clark when it comes to personality.

“Not the most talkative guy,” Ferentz said. “You’ve got to pry it out of him every now and then.”

If Castro’s no-nonsense, hard-hitting style works for him in Latrobe, he could put himself in position to be the Beanie Bishop Jr. of this summer. Bishop was also a sixth-year prospect who had a decent amount of draft buzz but didn’t hear his name called.

Instead, Bishop signed with the Steelers and seized his opportunity as a slot cornerback. Castro’s draft party also ended with him and his agent picking a team rather than a team picking him, but the champagne was popped nonetheless.

“It’s all fun, man,” Castro said last month during OTAs. “I’m here in the NFL, doing what I always wanted to do. I wake up every day and realize that I’m blessed. It’s fun going into work.”

Work’s about to get a lot harder now under the hot sun that beats down on Chuck Noll Field. Castro will be scratching and clawing to make it two years in a row that an undrafted rookie makes the team.

None managed to do so in 2023 after Jaylen Warren burst onto the scene at Saint Vincent College the year before. But most training camps have at least one pleasant surprise who opens eyes, from Bishop and Warren to James Pierre, or names of yesteryear such as Ola Adeniyi, Eli Rogers and Mike Hilton.

“I’m not even trying to worry about that or think about that too much,” Castro said. “I’m just glad I’m playing football right now.”

Castro, who ran a 4.59-second 40-yard dash at the combine, might not have enough range to play Fitzpatrick’s vacated role in the post. But he called the Steelers’ safety spots “interchangeable,” and Ferentz believes Castro can play anywhere in the secondary other than outside cornerback.

Ferentz also likes to hear that Castro seems to understand the significance of special teams. For rookies, particularly those who weren’t drafted, defensive snaps can be hard to come by in practice. But Castro wasn’t lamenting a lack of opportunities or in the spring, nor did he mind the football-in-shorts setting that doesn’t exactly accentuate his physicality.

“No, there’s so many different ways where you can show how you stand out,” Castro said. “Iowa, they taught me how to carry myself professionally. Everything matters when you walk in the building — how you present yourself, how you go about your work. There’s no hiding. On the field, everything’s gonna show. The tape tells your story.”

That’s the Mike Tomlin message that has stood out most so far to Castro. But he could apply to any number of Tomlin-isms.

Castro had no choice but to smile in the face of adversity after going undrafted. There was no seeking comfort when he barely played until his redshirt junior year of college. And if you suggest that it might be surreal for Castro to walk the same halls and wear the same jersey as a guy named Polamalu, he doesn’t blink.

“Surreal? I mean, as you get older and your dream becomes a reality out here, I feel like it’s not that little kid feeling,” Castro said. “It’s not the same. It’s just feeling grateful.”