What new call-up William Kempner brings to Miami

MIAMI, FL — The Miami Marlins designated starting pitcher Chris Paddack for assignment on Tuesday following a short and difficult tenure with the club. In seven appearances (six starts), Paddack had an 0–5 record and an ERA above seven. In a corresponding move, Miami recalled right-handed pitcher William Kempner, who is now in line to make his MLB debut during this series against the Baltimore Orioles.

Kempner was acquired from the San Francisco Giants in January 2025 in exchange for international bonus pool money. This season with Triple-A Jacksonville, he has posted a 6.46 ERA and a 4.15 FIP, along with an eye-popping 19.96 K/9. His 47.9 percent strikeout rate ranks second in the International League. However, control issues have prevented him from reaching his full potential, as Kempner acknowledged when speaking with reporters.

“I get a little erratic sometimes, but I’m working on it. If I can get the strikeouts with the walks, then we’re going to be okay,” Kempner said.

In his most recent appearance on May 1, Kempner threw two innings of no-hit baseball with two strikeouts and touched 96.0 mph on his fastball. It was only the third time in 12 games this season that he didn't allow any baserunners.

Kempner also shared that he was pranked by his coaches when they shared the news of his promotion to the big leagues. 

“I was on the phone with my pitching coach [Jerad Eickhoff]. I missed his call, and then I called him back, and he told me to come in and throw a bullpen tomorrow. Then he said he was just messing with me and that I was going to the big leagues. There’s no one I’d rather get that call from than him and our manager, (David Carpenter). Two amazing dudes.”

William Kempner spoke to the media today#Marlins pic.twitter.com/tZRGxpGwnX

— Kevin Barral (@kevin_barral) May 5, 2026

Marlins manager Clayton McCullough spoke highly of Kempner’s arsenal.

“I think it’s going to be a tough look for hitters. It’s a big fastball with movement both ways, and he has a very good breaking ball. We know he has the ability to miss bats. He’s shown that in Triple-A. Ultimately, his ability to fill up the strike zone consistently is going to determine how well he performs here.”

McCullough confirmed that the Marlins will be calling up a starting pitcher on Friday (most likely Robby Snelling) to fill Paddack's rotation spot. Barring a sudden injury to somebody on the pitching staff, Kempner is the main candidate to go back down to AAA at that time.

Between now and then, Kempner looks to fill a role in the bullpen, specifically against right-handed batters. I am optimistic about Kempner as his arsenal has lots of potential, with just walks hindering him.