When Kumar Rocker makes his big league debut for the Rangers on Thursday, a prospect path that has featured more ups and downs than most will reach a new high.

Just 16 months ago, Rocker blew out his elbow pitching in High-A and required Tommy John surgery. He didn't return to game action until this July, when he gave up eight runs in seven innings during three outings in the Rookie-level Arizona Complex League.

Since then, he has been as overpowering as any pitcher in the Minor Leagues. In 29 2/3 innings over seven starts in Double-A and Triple-A, the right-hander struck out 47 while allowing just 17 baserunners and three runs for a 0.91 ERA, pitching his way onto MLB Pipeline's Top 100 Prospects list. More important, he recaptured the stuff that made him a sensation as a Vanderbilt freshman in 2019.

No. 95 on the Top 100, Rocker is sitting at 97-98 mph and touching 100 mph with his fastball, working mostly with a four-seamer but also mixing in a two-seamer that has been an effective chase pitch. Nevertheless, his heater still takes a back seat to his signature pitch, a wipeout slider in the mid-80s. It's a small sample size to be sure, but Triple-A hitters swung at 30 of his sliders and failed to make contact on 23 of them (77 percent).

“He's been dealt some challenging circumstances with things that were outside of his control,” Texas assistant GM Ross Fenstermaker told MLB.com's Kennedi Landry. “But I think the biggest takeaway with Rock is he's just so strong-willed and determined to achieve what he wants to achieve. He's really built to handle adversity in a very high capacity. It's impressive what he does and how he goes about it. I’m glad he’s a Ranger.”

Rocker turned down first-round overtures from clubs as a Georgia high schooler in 2018 because he wanted to attend Vanderbilt, where he made an immediate impact. He threw a 19-strikeout no-hitter against Duke in an elimination game in the NCAA super regionals, then earned two victories and Most Outstanding Player honors at the 2019 College World Series to lead the Commodores to the national championship.

After the pandemic truncated the 2020 college season, Rocker led NCAA Division I in victories (14) and strikeouts (179 in 122 innings, tying teammate Jack Leiter) in 2021 while helping Vanderbilt finish second at the CWS. But his velocity fluctuated throughout the season, leading to questions about his health. He agreed to a $6 million bonus after the Mets selected him 10th overall in the Draft, only to have New York pull the deal after a post-Draft physical revealed concerns about his shoulder and elbow.

Rocker quietly had shoulder surgery in September 2021 -- an operation that teams didn't find out about until the following spring, when he flashed high-end stuff in controlled outings in the independent Frontier League. The Rangers stunned the industry by selecting him third overall in July 2022, signing him for an under-slot $5.2 million and using the savings to give their next pick (Brock Porter) a fourth-round record $3.7 million.

Rocker underwhelmed in his first pro action in the Arizona Fall League after the 2022 season. He had one of the best sliders in the developmental circuit, but he struggled to throw strikes or miss bats with his fastball and his arm slot was notably lower than usual. He looked much better operating from a higher slot in 2023, striking out 42 in 28 innings in High-A before his elbow gave out.

If Rocker can stay healthy, he can be the frontline starter everyone assumed he would become while watching him star as a Vanderbilt freshman. Though he relies mostly on his fastballs and slider, he also has a plus low-80s curveball and an average low-90s changeup with fade. He comes with a history of throwing strikes and an extremely physical 6-foot-5, 245-pound frame.

Rocker's results during his September callup won't matter much. His promotion is more about getting him acclimated to the big leagues and laying the groundwork for him to compete for a rotation job next spring.