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William Kempner

#71 - Relief Pitcher

Miami Marlins

Bats / Throws Right / Right
Date of Birth 6/18/2001 (25)
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 12.1 2.92 0.97 28.0% 8.0%
221st 3
Sv
351st 52.0
IP
63rd 4.19
ERA
22nd 1.34
WHIP
58th 22.7%
K%
111th 9.8%
BB%
FB MPH SwStr% CSW% Str-ICR MTK% PLV PLA
95.5 15.6% 33.7% 53.8% 5.5% 4.77 3.97
132nd 94.7
FB MPH
39th 12.2%
SwStr%
10th 28.5%
CSW%
72nd 51.2%
Str-ICR
249th 4.7%
MTK%
303rd 4.94
PLV
253rd 3.56
PLA

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 9 0 12.1 1-0 0 0 2.92 0.97 4.10 3.35 3.46 3.97 28.0% 8.0% 5.8 0.73 .241 16.7% 79.4% 33.3% 30.0% 15.6% 33.7% 0.65 4.77
RP MLB Percentile 1 0 0 12-85 0 0 82 93 50 79 85 27 83 67 93 70 87 49 79 77 5 88 97 90 12
RP MLB AVG 42 2 52.0 3-3 3 7 4.19 1.34 4.16 4.17 4.24 3.56 22.7% 9.8% 8.3 1.08 .291 17.6% 72.5% 36.8% 44.0% 12.2% 28.5% 0.50 4.94
Career 9 0 12.1 1-0 0 0 2.92 0.97 4.10 3.34 3.45 3.97 28.0% 8.0% 5.8 0.73 .241 16.7% 79.4% 33.3% 30.0% 15.6% 33.7% 0.65 4.77

William Kempner Repertoire

2026 All
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William Kempner Game Log

William Kempner Standard

Hide 2026 MLB Percentile | Hide 2026 MLB Average
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 9 0 12.1 1-0 0 0 0 199 127 72 50 8 5 2 0 1 14 4 2 0
RP MLB Percentile 1 0 0 12-85 0 0 0 0 0 100 0 100 100 93 50 92 3 99 46 78
RP MLB AVG 42 2 52.0 3-3 0 3 7 884 565 319 227 48 32 9 1 6 52 21 3 2
Career 9 0 12.1 1-0 0 0 0 199 127 72 50 8 5 2 0 1 14 4 2 0

William Kempner Advanced

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Year Team K% BB% AVG SLG OPS wOBA BABIP BACON xAVG xwOBA xBABIP xwoBACON EV FB EV LA xERA
2026 MIA 28.0% 8.0% .182 .295 .575 .265 .241 .267 .239 .316 .326 .384 85.8 94.2 17.9 4.10
RP MLB Percentile 83 67 94 88 87 84 87 88 45 50 7 25 83 2 18 50
RP MLB AVG 22.7% 9.8% .241 .389 .712 .314 .291 .321 .235 .314 .280 .358 87.6 89.3 13.1 4.16
Career 28.0% 8.0% .182 .295 .575 .265 .241 .267 .239 .316 .326 .384 85.8 94.2 17.9 4.10

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 MIA48.2% (95.5)14.6% (94.0)12.6% (87.3)-22.1% (81.6)-2.5% (86.8)-- 62.8% 37.2%
RP MLB Percentile 73 (62) 25 (46) 32 (22) - 58 (35) - 4 (55) - - 86.0% 14.0%
RP MLB AVG 38.7% (94.7) 26.6% (94.1) 19.6% (89.4) 25.9% (86.1) 20.7% (82.3) 15.3% (80.3) 17.7% (86.1) 18.9% (86.6) 42.7% (61.5) 48.7% 51.2%
Career48.2% (95.5)14.6% (94.0)12.6% (87.3)-22.1% (81.6)-2.5% (86.8)-- 62.8% 37.2%

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 MIA38.5% (16)20.7% (2)48.0% (4)-27.3% (9)-0.0% (0)-- 34.4% 32.4%
RP MLB Percentile 99 (66) 12 (83) 99 (62) - 41 (57) - 0 (0) - - 96.0% 78.9%
RP MLB AVG 27.2% (32) 27.6% (13) 26.9% (15) 29.7% (28) 28.4% (20) 27.3% (15) 22.3% (21) 22.6% (21) 19.3% (9) 27.9% 28.8%
Career38.5% (16)20.7% (2)48.0% (4)-27.3% (9)-0.0% (0)-- 34.4% 32.4%

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% 36.7% 20.0% 13.3% 50.0% 36.7% 30.0% 33.3% 15.1% 66.7% 26.7% 3.3% 3.3% 33.3%
RP MLB Percentile 5 0 21 78 0 21 19 95 7 80 27 84 91 77
RP MLB AVG 44.0% 21.7% 24.1% 10.2% 34.6% 40.9% 33.7% 25.4% 18.1% 63.0% 24.5% 5.8% 6.8% 36.8%
Career 30.0% 36.7% 20.0% 13.3% 50.0% 36.7% 30.0% 33.3% 15.1% 66.7% 26.7% 3.3% 3.3% 33.3%

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 .182 .265 .241 .267 .239 .316 .326 .384 85.8 94.2 17.9 16.7% 33.3% 20.0%
RP MLB Percentile 94 84 87 88 45 50 7 25 83 2 18 49 77 86
RP MLB AVG .241 .314 .291 .321 .235 .314 .280 .358 87.6 89.3 13.1 17.6% 36.8% 24.4%
Career .182 .265 .241 .267 .239 .316 .326 .384 85.8 94.2 17.9 16.7% 33.3% 20.0%

William Kempner Approach › Plate Discipline

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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 42.7% 63.8% 45.7% 30.7% 34.1% 15.1% 65.9% 73.2% 54.3% 18.1% 15.6% 33.7% 15.1% 59.8% 0.65 53.8%
RP MLB Percentile 27 47 30 43 94 7 94 98 72 77 88 97 19 70 90 79
RP MLB AVG 44.5% 63.8% 47.4% 31.7% 25.6% 18.1% 74.4% 83.9% 58.5% 16.4% 12.2% 28.5% 17.1% 58.3% 0.50 51.2%
Career 42.7% 63.8% 45.7% 30.7% 34.1% 15.1% 65.9% 73.2% 54.3% 18.1% 15.6% 33.7% 15.1% 59.8% 0.65 53.8%

William Kempner Approach › Locations

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Year Team Zone% aLoc% x-mLoc% gLoc% hiLoc% y-mLoc% loLoc% iLoc% oLoc% mmLoc%
2026 MIA 42.7% 50.3% 22.6% 27.1% 38.2% 27.6% 34.2% 34.2% 43.2% 6.5%
RP MLB Percentile 27 99 93 3 61 7 17 84 49 46
RP MLB AVG 44.5% 34.6% 27.0% 38.4% 36.2% 22.9% 40.9% 29.9% 43.1% 6.6%
Career 42.7% 50.3% 22.6% 27.1% 38.2% 27.6% 34.2% 34.2% 43.2% 6.5%

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 57.8% 12.6% 29.6% 11.3% 62.0% 52.0% 21.7% 22.0% 23.7%
RP MLB Percentile 36 37 45 9 56 62 58 13 87
RP MLB AVG 58.5% 12.1% 29.9% 14.5% 61.0% 50.1% 21.1% 26.7% 19.3%
Career 57.8% 12.6% 29.6% 11.3% 62.0% 52.0% 21.7% 22.0% 23.7%

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 199 4.77 39.7% 18.6% 41.7% -2.0% 5.5% -2.9 -1 3.97
RP MLB Percentile 0 12 3 70 7 7 25 68 53 27
RP MLB AVG 884 4.94 45.9% 17.3% 36.8% 9.1% 4.7% 0.6 -1 3.56
Career 199 4.77 39.7% 18.6% 41.7% -2.0% 5.5% -2.9 -1 3.97
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