Steelers release season-opening starter Juan Thornhill, claim safety Sebastian Castro

The Pittsburgh Steelers swapped out safeties on their active roster Monday, claiming intriguing undrafted rookie Sebastian Castro and releasing season-opening starter Juan Thornhill.

A former Super Bowl winner with the Kansas City Chiefs, Thornhill played 92% of the Steelers defensive snaps over the first two games of the season but had been getting phased out over the past month. He was limited to special-teams duty the past two games after the trade acquisition of Kyle Dugger.

Thornhill, who turned 30 last month, signed a one-year, $3 million free-agent contract with the Steelers in March with the idea he would replace Damontae Kazee at free safety. Thornhill had spent the previous two seasons with the Cleveland Browns but was not living up to the three-year, $21 million deal he’d signed with them in 2023.

A former second-round pick of Kansas City who made 52 starts for the perennially contending Chiefs over four seasons there, Thornhill infamously during this training camp said the 2025 Steelers defense could be “one of the best of all time.”

In nine games with the Steelers, he had one pass defense, one fumble recovery and 38 tackles (23 solo, one for loss).

In Castro, the Steelers are re-acquiring a player they signed out of Iowa after the draft ended in April. Castro had a good training camp and was on the Steelers’ practice squad when the regular season began. The Tampa Bay Buccaneers, though, signed him to their active roster Sept. 30.

The 5-foot-11, 203-pound Castro was in uniform for one game with the Bucs — Oct. 12 against San Francisco — and made one tackle over six special-teams snaps. Castro was second- and third-team all-Big Ten, respectively, the past two seasons.