Scouting Report
Updated May 20, 2026
William Kempner, 24-year-old right-handed pitcher from San Jose, California, made his MLB debut on May 5, 2026, for the Miami Marlins against the Baltimore Orioles. In his debut appearance, he pitched a perfect eighth inning using just eight pitches, recording one strikeout, one fly out, and one groundout. He was optioned back to Triple-A Jacksonville on May 6 to make room for another bullpen arm (Dax Fulton). Kempner was originally drafted by the San Francisco Giants in the third round of the 2022 MLB Draft out of Gonzaga University. He missed the entire 2024 season due to a broken foot and was traded to the Marlins in January 2025. Prior to his call-up, he had strong performance in Triple-A Jacksonville with 34 strikeouts in 15.1 innings pitched across 12 games, and previously went 3-0 with a 2.65 ERA in 13 games during the 2025 season.
Strengths
- + Perfect debut inning with efficient pitch count (8 pitches)
- + Strong strikeout ability demonstrated in minors (34 K in 15.1 IP)
- + Successful progression through minor league system (High-A to Double-A to Triple-A)
- + Helped Jacksonville Jumbo Shrimp win Triple-A National Championship
- + Low ERA in Triple-A (2.65 in 13 games)
- + Unique sidearm delivery providing competitive advantage
- + Third-round draft pick pedigree from reputable program (Gonzaga)
- + Young age (24) with room for development
About
William Kempner is a rp for the Miami Marlins.
Player Overview
RP
Miami Marlins