Pittsburgh Steelers’ best rookie sleeper to make impact in 2025 NFL season

The Pittsburgh Steelers selected seven players in the 2025 NFL Draft but made one of their most intriguing additions after the event concluded. After going unclaimed, former Iowa safety Sebastian Castro signed with the Steelers as an undrafted rookie.

Despite being a two-time All-Big 10 defender, Castro’s lack of size and speed caused all 32 teams to pass on him across seven rounds. He was invited to the NFL Draft Combine but did not perform well, running a 4.59-second 40-yard dash and recording an unimpressive 30.5-inch vertical jump. Without a reputation as a concussive hitter, Castro had no redeeming qualities in his physical profile to make him a prospect worth shedding millions for.

Regardless of his limited athleticism, Castro was still a popular post-draft target as one of the best safeties in the Big 10 over the past two years. He ended up landing with the Steelers, where he has a chance to not only make the team, but realistically carve out a meaningful role as a rookie.

Like any undrafted prospect, Castro’s biggest test will come in the offseason. Once he survives rookie minicamp, he will be put to the test in Pittsburgh’s training camp, before facing one final hurdle in the preseason. Still, with the Steelers lacking youth and depth in the secondary, Castro has an open road to surviving roster cuts and being the team’s biggest surprise in 2025.

Sebastian Castro will make final roster

With Minkah Fitzpatrick and DeShon Elliott anchoring their secondary, the Steelers are not in the market for another safety. That was evident in the 2025 NFL Draft, in which Pittsburgh took five defenders, but no safeties. General manager Omar Khan spent his final pick in the seventh round on cornerback Donte Kent, but did not add any new talent to his safety room.

However, behind Fitzpatrick and Elliott, the Steelers only have four reserve safeties on their current roster, including Castro. Veteran Juan Thornhill headlines the bench group, but Castro is essentially the only strong safety on the team aside from Elliott. While the Steelers love two-high safety looks, Mike Tomlin still deploys a lot of traditional single-high safety sets.

Castro might lack the speed and man coverage skills to play free safety in the NFL, but his physical play style still gives him the chance to be an asset near the line of scrimmage. Whether he takes the field as a nickelback or blitzing strong safety, the Steelers can find ways to use him. In his final three years at Iowa, Castro racked up 163 tackles, including 14 behind the line of scrimmage.

Castro’s athletic limitations prevent him from being an every-down player for the time being, but his tenacity as a run-stopper makes him more than just a special teams contributor. It may take him a while, but if given the opportunity, Castro can be a pleasant surprise for a secondary that struggled with injuries in 2024. Similar hustle players always find a way to squeeze into the final roster and eventually onto the field.

Steelers need help on special teams

If nothing else, Castro should be able to immediately make an impact on special teams. Though easily the least respected aspect of the game, Pittsburgh could certainly use the help after struggling in kick coverage a year ago.

In the first year of the new dynamic kickoff, the Steelers allowed 28.9 yards per return, the seventh-most in the league. They defended slightly better in punt coverage but still ranked in the bottom half of the league.

While not a special teamer in college, Castro profiles as a player who will have an impact in that regard at the next level. He does not have the speed of a gunner, but his pursuit and aggressiveness as a tackler would help any team on kickoffs.

Stars are rarely made on special teams, but they provide a potentially lucrative avenue to field time for undrafted players like Castro. Unless an injury somehow thrusts Castro into the starting lineup, he should be a menace in special teams all season long and lift the team’s prior struggles to defend returns.