2027 South Side Sox Top Prospect No. 91: Jonathan Clark

Jonathan Clark was really good for the Birmingham Barons in 2026 — but he’s been simply brilliant this fall with the AZFL’s Glendale Desert Dogs. | (Photo by Brandon Sloter/Getty Images) Jonathan ClarkRight-Handed Relief Pitcher6´1´´190 poundsAge: 262026 South Side Sox Top 100 ranking522026 High Level Birmingham (AA)Age relative to high level +1.4 yearsSSS rank among all right-handed relievers in the system 16Overall 2026 stats (High-A/AA/AZFL) 9-3 ⚾️ 57 games (34 finishes) ⚾️ 9 SV ⚾️ 3.99 ERA ⚾️ 1.404 WHIP ⚾️ 70 K ⚾️ 33 BB ⚾️ 1.0 WARJonathan Clark is one of the odder success stories in the White Sox system.The San Jose State product was signed as an undrafted free agent not in July after the draft … but more than two years after Clark’s draft class matriculated. So when the White Sox inked Clark on Feb. 12, 2025, there was little in his history as a five-year starter for the Spartans that would indicate real success in anything more than semipro ball. And frankly, pitching for the Glacier Range Riders and Missoula PaddleHeads in 2023 and 2024 (independent Pioneer League ball) didn’t move the needle at all, either (8.68 ERA over 25 games over the two seasons).Clark opted to work with Tread Athletics in order to retool his arm motion. The trainers put together a series of exercises on and off of the mound intending to create more flexibility and overall range of motion in his shoulder. His drills, including weighted balls and even larger-sized softballs, eased Clark away from pulling up short in his motion, which tightened his command and control.The White Sox put season statistics aside and liked what they saw, and boy did Clark pay back the faith with a phenomenal 2025. While pitching significantly old for his A-ball levels, Clark mowed down batters like he hadn’t done since … ever (OK, maybe high school). He filled a closer/high-leverage role in Kannapolis to start the season, and his 2.48 ERA and overall mature approach on the mound earned him a post-draft July call-up to Winston-Salem. And once there, Clark got even better, starving High-A batters to the tune of one earned run and seven hits over 14 ⅓ innings.Clark had a strong follow-up to his pro debut, starting 2026 in Winston-Salem but vacating for Double-A ball as May dawned. He spent the rest of 2026 as Birmingham’s primary closer, sharing the gig with Jackson Kelley but getting more high-leverage opportunities. And Clark, despite a bit of an elevated ERA and WHIP, passed with flying colors. An end-of-season gig in the Arizona Fall League only bolstered his final season numbers, as the righty has been immaculate in the thin air, named to the Fall Stars team and edging his ERA below 4.00.So why is Clark ranked so low, especially given his middle placement a year ago? I can’t tell you, other than to say ranking is a fickle game. I’ll go on record saying Clark places much too low on our list this year.One tug against Jonathan is his “advanced age,” as he’s yet to pitch a single inning in the White Sox system where he wasn’t older than his competition — and to that end, significantly older. Given he will assuredly start 2027 in Charlotte, Clark’s streak as a graybeard will end, one step from the South Side.Full 2027 South Side Sox Top 100 White Sox ProspectsStorystream