Athletics Claim Joe Rock From White Sox

The Athletics announced this afternoon that they’ve claimed left-hander Joe Rock off waivers from the White Sox. They quickly optioned him to Triple-A Las Vegas. To clear a 40-man roster spot for Rock, the team transferred right-hander Justin Sterner to the 60-day injured list.

The White Sox designated Rock for assignment two days ago after a three-month stint in the organization. He appeared in four games from June 13-24, allowing four earned runs in 10 1/3 innings with 12 strikeouts. Rock also allowed 11 walks in that sample, and he also hit two batters and threw a wild pitch. Largely due to those control issues, the lefty had a 5.65 SIERA and 6.84 expected ERA in his limited action, putting his true talent several runs higher than his 3.48 ERA.

The results haven’t been much better at Triple-A. In 32 2/3 innings for the Rays and White Sox’ top affiliates, Rock has a downright dreadful 6.89 ERA and 18.1% walk rate. To his credit, he has an excellent 28.1% strikeout rate and 50.6% ground ball rate in the minors. Opponents are also batting .407 on balls in play off Rock, which is untenably high. Poor batted ball fortune is only a partial explanation for his struggles, though, as Rock has simply allowed too many baserunners for his strikeout and ground ball tendencies to make a meaningful difference.

For now, there’s little harm in the A’s stashing Rock in Las Vegas as a depth piece. The big league bullpen ranks 19th in the Majors by strikeout rate (21.6%) and 28th by ground ball rate (38.4%). Rock could theoretically help in both of those areas, though he’d obviously need to get the walks under control in order to stick long-term. He posted much more manageable walk rates of 5.7% and 9.3% in 2024 and 2025, respectively, so perhaps there’s room for positive regression as he gets settled at Triple-A.

Sterner’s move to the 60-day IL was expected after he underwent season-ending right knee surgery two days ago. He was a decent bullpen arm last year, as he tossed 65 frames with a 3.18 ERA and an 18.4% K-BB rate. Sterner kept that up through his first 34 innings this year, but he imploded in his last 7 1/3 innings, allowing 13 earned runs in that time. As a result, he’ll finish the season with an ERA over 6.00 and having allowed 2.32 home runs per nine innings. He figures to return when healthy in 2027.