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William Kempner

#71 - Relief Pitcher

Miami Marlins

Bats / Throws Right / Right
Date of Birth 6/18/2001 (24)
Height, Weight 6'0", 222 lb
Hometown San Jose, CA

2026 Season Stats

Needs more playing time to qualify
MLB Rank MLB Average
Sv IP ERA WHIP K% BB%
0 9.0 0.00 0.56 30.3% 6.1%
- 2
Sv
- 25.0
IP
- 4.40
ERA
- 1.39
WHIP
- 22.2%
K%
- 10.3%
BB%
FB MPH SwStr% CSW% Str-ICR MTK% PLV PLA
95.6 16.2% 35.4% 57.7% 5.4% 4.85 3.31
- 94.3
FB MPH
- 12.0%
SwStr%
- 28.4%
CSW%
- 50.5%
Str-ICR
- 4.6%
MTK%
- 4.93
PLV
- 3.58
PLA
Holds List
Rank
91st

Articles

6/16/2026Fantasy Baseball Relief Pitcher Roundup: 6/15Rick Graham

6/16/2026Relief Pitcher Streamer Rankings Fantasy Baseball: 6/16Rick Graham

6/15/2026Relief Pitcher Streamer Rankings Fantasy Baseball: 6/15Rick Graham

6/14/2026Relief Pitcher Streamer Rankings Fantasy Baseball: 6/14Rick Graham

6/13/2026Relief Pitcher Streamer Rankings Fantasy Baseball: 6/13Rick Graham

See More Articles
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William Kempner Overview

Hide 2026 MLB Percentile | Hide 2026 MLB Average
Year Team G GS IP W-L Sv Hld ERA WHIP xERA FIP xFIP PLA K% BB% H/9 HR/9 BABIP HR/FB% LOB% ICR% GB% SwStr% CSW% IPR% PLV
2026 MIA 6 0 9.0 1-0 0 0 0.00 0.56 2.05 1.88 2.68 3.31 30.3% 6.1% 3.0 0.00 .150 0.0% 100.0% 25.0% 30.0% 16.2% 35.4% 0.71 4.85
RP MLB Percentile - - - --- - - - - - - - - - - - - - - - - - - - - -
RP MLB AVG 20 1 25.0 1-1 2 3 4.40 1.39 4.37 4.35 4.41 3.58 22.2% 10.3% 8.5 1.11 .292 17.9% 72.3% 37.4% 43.4% 12.0% 28.4% 0.49 4.93
Career 6 0 9.0 1-0 0 0 0.00 0.56 2.05 1.88 2.68 3.31 30.3% 6.1% 3.0 0.00 .150 0.0% 100.0% 25.0% 30.0% 16.2% 35.4% 0.71 4.85

William Kempner Repertoire

2026 All
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William Kempner Game Log

William Kempner Standard

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Year Team G GS IP W-L QS Sv Hld P Strikes Balls TBF H 1B 2B 3B HR K BB HB WP
2026 MIA 6 0 9.0 1-0 0 0 0 130 85 45 33 3 3 0 0 0 10 2 1 0
RP MLB Percentile - - - --- - - - - - - - - - - - - - - - -
RP MLB AVG 20 1 25.0 1-1 0 2 3 428 272 157 110 23 15 4 0 3 24 11 1 1
Career 6 0 9.0 1-0 0 0 0 130 85 45 33 3 3 0 0 0 10 2 1 0

William Kempner Advanced

Hide 2026 MLB Percentile | Hide 2026 MLB Average
Year Team K% BB% AVG SLG OPS wOBA BABIP BACON xAVG xwOBA xBABIP xwoBACON EV FB EV LA xERA
2026 MIA 30.3% 6.1% .100 .100 .282 .146 .150 .150 .181 .225 .271 .265 82.6 90.5 19.8 2.05
RP MLB Percentile - - - - - - - - - - - - - - - -
RP MLB AVG 22.2% 10.3% .243 .393 .722 .320 .292 .322 .239 .323 .283 .364 87.8 89.4 13.3 4.37
Career 30.3% 6.1% .100 .100 .282 .146 .150 .150 .181 .225 .271 .265 82.6 90.5 19.8 2.05

William Kempner Pitch › Mix

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Year Team FF% (MPH) SI% (MPH) FC% (MPH) SL% (MPH) ST% (MPH) CB% (MPH) CH% (MPH) FS% (MPH) KN% (MPH) Fastball% Secondary%
2026 MIA 49.2% (95.6) 12.3% (94.0) 10.8% (87.5) - 25.4% (81.7) - 2.3% (87.4) - - 61.5% 38.5%
RP MLB Percentile - - - - - - - - - - -
RP MLB AVG 37.6% (94.3) 25.6% (94.0) 21.8% (89.3) 26.0% (85.4) 21.7% (82.5) 17.6% (79.9) 18.2% (86.2) 19.8% (86.5) 31.8% (68.1) 47.7% 52.2%
Career 49.2% (95.6) 12.3% (94.0) 10.8% (87.5) - 25.4% (-) - 2.3% (87.4) - - 61.5% 38.5%

William Kempner Pitch › Results

Hide 2026 MLB Percentile | Hide 2026 MLB Average
Year Team FF CSW% SI CSW% FC CSW% SL CSW% ST CSW% CB CSW% CH CSW% FS CSW% KN CSW% Fastball CSW% Secondary CSW%
2026 MIA 42.2% (10) 12.5% (1) 57.1% (3) - 27.3% (7) - 0.0% (0) - - 36.3% 34.0%
RP MLB Percentile - - - - - - - - - - -
RP MLB AVG 27.0% (15) 27.4% (6) 27.0% (8) 29.3% (13) 28.2% (11) 27.5% (7) 21.9% (10) 24.2% (13) 23.3% (6) 27.6% 28.8%
Career 42.2% (10) 12.5% (1) 57.1% (3) - 27.3% (7) - 0.0% (0) - - 36.3% 34.0%

William Kempner Batted Ball › Contact

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Year Team GB% LD% FB% PU% SS% Pull% Cent% Oppo% Foul Str% PC% Fl&B% Solid% Brl% ICR%
2026 MIA 30.0% 35.0% 15.0% 20.0% 40.0% 50.0% 15.0% 35.0% 14.6% 75.0% 25.0% 0.0% 0.0% 25.0%
RP MLB Percentile - - - - - - - - - - - - - -
RP MLB AVG 43.4% 22.0% 24.3% 10.3% 34.8% 41.4% 33.4% 25.2% 17.8% 62.2% 24.6% 5.9% 7.3% 37.4%
Career 30.0% 35.0% 15.0% 20.0% 40.0% 50.0% 15.0% 35.0% 14.6% 75.0% 25.0% 0.0% 0.0% 25.0%

William Kempner Batted Ball › Outcomes

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Year Team AVG wOBA BABIP BACON xAVG xwOBA xBABIP xwoBACON EV FB EV LA HR/FB ICR% IPA%
2026 MIA .100 .146 .150 .150 .181 .225 .271 .265 82.6 90.5 19.8 0.0% 25.0% 15.2%
RP MLB Percentile - - - - - - - - - - - - - -
RP MLB AVG .243 .320 .292 .322 .239 .323 .283 .364 87.8 89.4 13.3 17.9% 37.4% 24.8%
Career .100 .146 .150 .150 .181 .225 .271 .265 82.6 90.5 19.8 0.0% 25.0% 15.2%

William Kempner Approach › Plate Discipline

Hide 2026 MLB Percentile | Hide 2026 MLB Average
Year Team Zone% Str% Swing% O-Sw% Whiff% Foul Str% Con% Z-Con% O-Con% CS% SwStr% CSW% BIP% PLUS% IPR% Str-ICR
2026 MIA 41.5% 65.4% 46.2% 32.9% 35.0% 14.6% 65.0% 74.3% 52.0% 19.2% 16.2% 35.4% 15.4% 63.1% 0.71 57.7%
RP MLB Percentile - - - - - - - - - - - - - - - -
RP MLB AVG 44.5% 63.3% 46.8% 31.1% 25.5% 17.8% 74.5% 83.9% 58.7% 16.5% 12.0% 28.4% 17.0% 57.8% 0.49 50.5%
Career 41.5% 65.4% 46.2% 32.9% 35.0% 14.6% 65.0% 74.3% 52.0% 19.2% 16.2% 35.4% 15.4% 63.1% 0.71 57.7%

William Kempner Approach › Locations

Hide 2026 MLB Percentile | Hide 2026 MLB Average
Year Team Zone% aLoc% x-mLoc% gLoc% hiLoc% y-mLoc% loLoc% iLoc% oLoc% mmLoc%
2026 MIA 41.5% 47.7% 23.8% 28.5% 38.5% 25.4% 36.2% 37.7% 38.5% 6.2%
RP MLB Percentile - - - - - - - - - -
RP MLB AVG 44.5% 34.7% 26.9% 38.4% 36.3% 22.9% 40.8% 30.1% 43.0% 6.5%
Career 41.5% 47.7% 23.8% 28.5% 38.5% 25.4% 36.2% 37.7% 38.5% 6.2%

William Kempner Approach › Counts

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Year Team Early% Behind% 2-Str% Early BIP% F-Str% TF-Str% ECS% 2-Str O-Sw% PAR%
2026 MIA 56.9% 13.8% 29.2% 10.8% 60.6% 48.5% 21.6% 28.9% 26.3%
RP MLB Percentile - - - - - - - - -
RP MLB AVG 58.5% 12.5% 29.6% 14.3% 60.3% 49.7% 21.2% 26.2% 19.1%
Career 56.9% 13.8% 29.2% 10.8% 60.6% 48.5% 21.6% 28.9% 26.3%

William Kempner PLV

Hide 2026 MLB Percentile | Hide 2026 MLB Average
Year Team P PLV QP% AP% BP% Q-BP% MTK% HP HL PLA
2026 MIA 130 4.85 41.5% 20.0% 38.5% 3.1% 5.4% -5.6 -3 3.31
RP MLB Percentile - - - - - - - - - -
RP MLB AVG 428 4.93 46.0% 17.1% 36.9% 9.1% 4.6% 0.8 +0 3.58
Career 130 4.85 41.5% 20.0% 38.5% 3.1% 5.4% -5.6 -3 3.31
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