Cardinals Rookie Lefty Experiences Impressive Highs, Humbling Lows in First MLB Outings

Making his first Busch Stadium appearance on Saturday and trying to repeat the flawless domination he flashed in his MLB debut six days earlier, St. Louis Cardinals’ rookie left-hander Cooper Hjerpe instead endured an outing about as unorthodox and funky as his herky-jerky throwing motion.

One great appearance, then one rather rocky one for the 25-year-old Hjerpe, who was still trying to figure out where things went so awry some 90 minutes after the Cardinals 6-5 loss to the White Sox on Saturday night. Such is life as an MLB rookie, and for a Cardinals club that came into Sunday first in the National League in games played (548), hits (367), runs scored (207) and homers (49) by first-year big-league players.

“Obviously, last Sunday was a really great high and today was a really low, and you don’t want to push yourself into doing something you’re not used to just because of one bad outing,” said Hjerpe, whose rough outing played a role in the Cardinals squandering 3-0 and 4-1 leads on Saturday. “You definitely can be pissed (rather than remaining calm) because it’s not like you are going to be happy after an outing like that. Obviously, I am going to give myself 15-to-30 minutes to be pissed about it but tomorrow is a new day and a new opportunity.”

In a span of 11 hitters faced over two innings on Saturday, Hjerpe allowed just two balls to be put in play – both hits – but he threw only 25 strikes among his 52 pitches. He struck out two, but the rest of the outing was badly disjointed with two hit two batters, four walks and two bases loaded free passes. In all, Hjerpe was tagged for four earned runs.

Unfortunately for Hjerpe, it was a regression to the lack of command he showed at times over his 15 starts earlier this season while working his way back from Tommy John surgery in April of 2025.

“This is part of it with him, right? We saw some of this (wildness) at times in the Minor Leagues, and we also saw the high ceiling of what his swing-and-miss (stuff) can look like,” Cardinals’ manager Oliver Marmol said. “At the big-league level, we’ve seen both sides of it.”

Six days earlier, Hjerpe had a debut for the ages when he pitched four perfect innings and struck out six in relief in a victory over the Colorado Rockies. It was the longest outing in an MLB debut without allowing a run since St. Louis native Max Scherzer went 4 1/3 innings in his first big-league game while pitching for Arizona.

With the Cardinals purposefully limiting the workload for starting pitcher Kyle Leahy – at 135 innings pitched he’s well beyond his career-most of 88 innings in 2025 – Hjerpe is being used in a “piggyback” manner on days when Leahy starts. That allows the Cardinals to keep Hjerpe on a routine similar to that of a starter – the role he had throughout his college stardom at Oregon State and over the last 3 ½ seasons in the Minor Leagues.

The downside, Marmol pointed out, is that the Cardinals are almost obligated to keep Hjerpe in the game to throw at least 50 pitches – even in games where he struggles to find the strike zone like Saturday night. Having him on the roster shortens the bullpen, so the Cards need him to work multiple innings on days when he enters out of the bullpen.

“Even if it doesn’t look good, you have to reach a certain threshold of pitches in order to maintain that (piggyback) workload,” Marmol said. “So, it can’t be a situation where the first inning looks bad and he doesn’t get past that 50 (pitch) mark and you take him out because you are trying to save that game. … With his personality, I think he’ll learn from it. He’ll slow it down more and make adjustments.”

That’s a process that Hjerpe was planning to address on Sunday morning to give himself the maximum amount of time to try and improve before his next outing on Friday against the Nationals.

“You have to find a way to flush (Saturday’s performance), look at the video and see if there’s anything there,” he said. “Maybe it was something physically and you go from there to fix it.

“During the game, you try to stay as external as you can because you don’t want to be thinking about mechanics then because that’s when things will go south. There were glimpses of (progress) in that first inning by working through that bases loaded jam, only allowing one run and striking out the side. But, it was a pretty bad night and we’re going to fix it and move forward.”