William Kempner

Career Stats, Bio & Records (2026)

William Kempner is a pitcher who has played in Major League Baseball since 2026 for the Miami Marlins. Across 9 career appearances, he has gone 1-0 with a 2.92 ERA and 14 strikeouts. His career Pitcher PIV — Baseball Data Hub's era-adjusted measure of pitching impact — is 258.0.

W (Wins):
Games credited to a pitcher whose team took a lead it never surrendered while he was the pitcher of record.
ERA (Earned Run Average):
Earned runs allowed per nine innings pitched: (ER × 9) ÷ IP. The primary measure of pitching effectiveness.
SO (Strikeouts):
For a batter, times retired on a third strike; for a pitcher, batters retired on a third strike.
WHIP (Walks and Hits per Inning Pitched):
Baserunners allowed per inning: (BB + H) ÷ IP. Under 1.00 is elite.

Data updated

Active Player
W–L 1–0
ERA 2.92
WHIP 0.97
SO 14
Pitcher PIV 258.0
Bats / Throws
R / R
Height / Weight
6'0" / 222 lb
Born
6/18/2001 in San Jose, CA, USA
MLB Debut
2026-05-05
Jersey
#71
Draft
2022

Full name: William Kempner Kempner

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Career Pitching Statistics

William Kempner — Career Pitching Statistics
W L G GS CG SHO SV IP H ER HR BB SO ERA Pitcher PIV
1 0 9 0 0 0 0 12.1 8 4 1 4 14 2.92 258.0

Career ERA 2.92 vs. league average 4.18 across their career seasons — 30.1% better than league average.

Season-by-Season Pitching

Pitching Career Arc

Click a stat to plot it across every season.

William Kempner — Season-by-Season Pitching
Year Team Lg W L G GS CG SHO SV IP H ER BB SO ERA Lg ERA Pitcher PIV
2026 MIA NL 1 0 9 0 0 0 0 12.1 8 4 4 14 2.92 4.18 (+30%) 258.0
Career · 1 season 1 0 9 0 0 0 0 12.1 8 4 4 14 2.92 — 258

Lg columns show the league average for that season, with the player's figure as a percentage above or below it. Career totals the seasons listed above.

William Kempner: the record in brief

The debut date in the bio is May 5, 2026; William Kempner is an active player, and this profile updates as the season goes on. Every season row on the page belongs to the Miami Marlins, in 2026. Height and weight on file: 6'0" and 222 pounds. Kempner was born on June 18, 2001, in San Jose, CA, USA.

Kempner's career pitching line is 1 win, 0 losses and a 2.92 ERA over 9 appearances. Kempner has 14 strikeouts. That 2.92 ERA compares with a 4.18 league average across the same seasons, 30.1% better. All of that pitching came in 2026, with 9 games and 14 strikeouts. Kempner's career Pitcher PIV, which scores run prevention against each season's league, is 258.0.

The draft line shows 2022.

Frequently Asked Questions about William Kempner

Is William Kempner a pitcher?
Yes. William Kempner has pitched in the major leagues, recording 1 wins and 14 strikeouts.
What teams has William Kempner played for?
William Kempner has played for one team, the Miami Marlins (2026).
What are William Kempner's career stats?
In 9 games, William Kempner has gone 1-0 with a 2.92 ERA, 14 strikeouts, and 12.1 innings pitched.
How tall is William Kempner and how much does he weigh?
William Kempner is listed at 6 feet and 222 pounds.
What number does William Kempner wear?
William Kempner wears number 71, according to MLB's 2026 roster data.
What is William Kempner's career ERA?
William Kempner has a 2.92 career ERA, with a 1-0 record and 14 strikeouts.
How many strikeouts does William Kempner have?
William Kempner has 14 career strikeouts.