Rookie Reliever Rides Unorthodox Throwing Motion to Huge Success Out of Cardinals Bullpen

All throughout Cooper’s Hjerpe’s baseball life, critics were skeptical and doubtful of his unorthodox, herky-jerky throwing motion from the left side – one where he delivers pitches from a three-quarters arm angle and, at times, it appears as if his elbow is on the verge of dislocating.

Even as Hjerpe piled up success at Woodland High School in Northern California and then Oregon State University, many wondered about the staying power of a delivery that seemed to put his arm, shoulder and elbow in awkward angles.

“Fortunately, he didn’t listen to me all the time,” Carl Hjerpe, a former pitcher at Cal Poly University, said in a recent interview. “I kept telling him, ‘Get your arm up, get on top of the ball,’ and he kept staying low. So, I’m glad he didn’t listen to me.”

Hjerpe, whose professional career was interrupted by arthroscopic elbow surgery in 2022 and stopped completely by an ulnar collateral ligament tear and Tommy John surgery that cost him all of 2025 and half of ’26, finally got the chance to show off the power of conviction in his different throwing motion in his MLB debut on Sunday in Colorado. Baffling MLB hitters who clearly had trouble picking up the ball from his lower arm slot, the 25-year-old lefthander pitched four perfect innings, struck out six in relief and nabbed his first MLB victory.

A Cardinals team that trailed 5-1 at the time of Hjerpe’s entry into the game seemed to gain momentum from him retiring the Rockies in order four straight times. The Cardinals scored six runs in the fifth inning to get him the lead, and then they effectively knocked him out of the game with a lengthy three-run eighth inning to build a big lead before hanging on to win 10-8.

As it turns out, Hjerpe’s success out of the bullpen in his debut was about as unique as his side-armed throwing motion. Hjerpe (1-0) authored the longest MLB relief outing in a debut without allowing a base runner since Arizona’s Max Kranick (five innings in 2021) St. Louis native Max Scherzer (4 1/3 innings in 2008). Also, he became the first Cardinals reliever to debut with six strikeouts in relief since Marshall Bridges did it in 1959 against the Phillies.

"Honestly, once I got onto the field, I wasn't too nervous because that's when things got rolling," said Hjerpe, a first-round draft pick in 2022 who had approximately 20 family members, friends and former baseball teammates in the stands to watch his debut on Sunday. "I was definitely locked in. The hardest part is like, between long innings, staying locked in. I just sat on that bench and did whatever I could to lock back in. Obviously, I was happy going four scoreless, and each inning I just got happier."

Clearly, the Rockies were none too happy trying to pick up the baseball from the unorthodox-throwing left-hander. By design, the first two batters Hjerpe faced were left-handers – Brett Sullivan and Vimael Machin – and there were retired on a slow roller to short and the first strikeout of the rookie’s career. Originally, Hjerpe’s 78.1 mph sweeper – one that featured 11 inches of horizontal break, per Baseball Savant – was called a ball, but the call was overturned when rookie catcher and former Triple-A teammate Leo Bernal requested a challenge.

From there, Hjerpe’s stuff only seemed to get nastier – even though he didn’t throw a pitch harder than 92.2 mph during his four innings of work. In the fifth, he ended an eight-pitch at bat by striking out Troy Johnson with a 78.4 mph sweeper that featured 12 inches of horizontal break. In the sixth, he caught standout rookie TJ Rumfield looking with a four-seam fastball that broke 15 inches horizontally and he punched out Mickey Moniak with another fastball.

With lefties 0 for 7 with four strikeouts against Hjerpe, the Rockies went to their bench for two right-handed batters in the seventh inning. All-Star Hunter Goodman managed an infield grounder off a changeup that featured 15 inches of horizontal break and Connor Norby struck out on a sweeper than broke in on his hands 13 inches. Hjerpe saved his hardest breaking pitch for his final hitter, and he fanned Ezekiel Tovar with a filthy changeup that cut away from the hitter some 17 inches, per Baseball Savant.

All of it, Hjerpe, was confirmation that sometimes an orthodox throwing motion can be a huge plus. Assuredly, he was tested along the way with arthroscopic elbow surgery in 2023, the Tommy John procedure in 2025 and the 15 Minor League rehab starts he made this season prior to his MLB promotion, but he came out on the other side of those hurdles stronger than ever.

“Everyone’s journey is different,” Hjerpe told MLB.com. “Mine had a lot of bumps in the road, man. Sometimes those things are out of your control.