First Marlins trade of 2025: William Kempner for international bonus pool money

[Ely Sussman]

Shortly after finalizing their 2025 international signing class, the Miami Marlins traded away a chunk of their leftover bonus pool money to acquire right-handed reliever William Kempner from the San Francisco Giants. Marc Delucchi reports that it's $250,000.

A third-round draft pick of the Giants in 2022, Kempner has been used mainly as a reliever in pro ball. Across four different minor league levels (primarily Low-A and High-A), he has posted a 3.89 ERA, 4.52 FIP and .227 BAA in 71 ⅔ career innings pitched. His 2024 campaign was wiped out by foot surgery, but he resurfaced with four appearances (3.2 IP) in the Arizona Fall League.

Kempner operates from a very low, practically sidearm release point. His arsenal includes a mid-90s fastball and low-80s sweeper. Several of the sweepers he threw in the AFL registered spin rates north of 2,900 RPM, which would be elite even by MLB standards.

Kempner is not yet on the 40-man roster. He will be Rule 5 Draft-eligible following the 2025 season. He's most likely to begin the year in Double-A Pensacola's bullpen.

Between their initial 17 signings and this trade, the Marlins have used up more than 92% of their bonus pool for the current international signing period.