Athletics claim off waivers Joe Rock from White Sox

The Athletics on Sunday claimed left-handed pitcher Joe Rock off waivers from the Chicago White Sox and immediately optioned him to Triple-A Las Vegas. The move required a corresponding 40-man roster adjustment, with right-hander Justin Sterner transferred to the 60-day injured list.

Rock, 26, spent only three months with the Chicago after the White Sox acquired him from the Tampa Bay Rays in May in exchange for infielder Oliver Dunn. Chicago designated Rock for assignment two days before the Athletics claimed him. During his short major league stint with the White Sox, Rock appeared in four games from June 13-24, covering 10 1/3 innings. He surrendered four earned runs while recording 12 strikeouts, but he also issued 11 walks, hit two batters and threw a wild pitch.

Those control problems have been a major issue for Rock throughout the 2026 season. His 3.48 ERA in the majors came alongside a 5.65 SIERA and a 6.84 expected ERA. At Triple-A, he has produced a 6.89 ERA across 32 2/3 innings while walking 18.1% of the 171 batters he faced. He also hit six batters in the minors, meaning 21.6% of opposing hitters reached base through either a walk or hit-by-pitch.

Rock has nevertheless shown some encouraging traits. His Triple-A work includes a 28.1% strikeout rate and a 50.6% ground-ball rate. Opponents have also hit .407 on balls in play against him. Before this season, Rock compiled a 4.79 ERA, 23.1% strikeout rate and 7.5% walk rate over 329 minor league innings from 2023 through 2025. He was moved into a primary relief role this year, although he remains optionable for the rest of 2026 and has another option year remaining.

For the Athletics, Rock provides a depth option at Triple-A. Their major league bullpen ranks 19th in MLB with a 21.6% strikeout rate and 28th with a 38.4% ground-ball rate, areas in which Rock has produced better minor league numbers. His ability to become a longer-term option will depend heavily on improving his control.

Sterner’s transfer to the 60-day IL follows season-ending right knee surgery. He finishes 2026 with an ERA above 6.00 and 2.32 home runs allowed per nine innings after giving up 13 earned runs over his final 7 1/3 innings.