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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%
213th 3
Sv
351st 43.0
IP
72nd 4.25
ERA
27th 1.35
WHIP
57th 22.5%
K%
113th 9.7%
BB%
FB MPH SwStr% CSW% Str-ICR MTK% PLV PLA
95.5 15.6% 33.7% 53.8% 5.5% 4.77 3.98
125th 94.6
FB MPH
42nd 12.2%
SwStr%
14th 28.5%
CSW%
76th 51.2%
Str-ICR
242nd 4.7%
MTK%
301st 4.94
PLV
255th 3.50
PLA

Articles

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6/11/2026Fantasy Baseball Relief Pitcher Roundup: 6/10Rick Graham

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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 4.09 3.33 3.45 3.98 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 3 0 0 19-81 0 0 79 92 51 78 84 27 84 66 90 69 82 49 78 75 6 86 95 89 12
RP MLB AVG 34 2 43.0 2-2 3 6 4.25 1.35 4.23 4.24 4.30 3.50 22.5% 9.7% 8.3 1.12 .289 17.7% 72.7% 37.0% 43.5% 12.2% 28.5% 0.50 4.94
Career 9 0 12.1 1-0 0 0 2.92 0.97 4.09 3.33 3.44 3.98 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

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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 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 3 0 0 19-81 0 0 0 0 0 100 0 99 100 87 44 90 7 97 36 73
RP MLB AVG 34 2 43.0 2-2 0 3 6 721 461 261 185 39 26 7 1 5 42 17 2 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 4.09
RP MLB Percentile 84 66 91 87 87 85 82 85 46 51 8 30 80 2 21 51
RP MLB AVG 22.5% 9.7% .241 .391 .713 .315 .289 .320 .236 .316 .280 .360 87.7 89.2 13.4 4.23
Career 28.0% 8.0% .182 .295 .575 .265 .241 .267 .239 .316 .326 .384 85.8 94.2 17.9 4.09

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 75 (63) 27 (49) 30 (20) - 57 (34) - 5 (53) - - 87.2% 12.5%
RP MLB AVG 38.3% (94.6) 26.4% (93.9) 20.2% (89.4) 25.7% (85.6) 21.3% (82.5) 16.4% (79.7) 17.2% (86.1) 17.5% (86.7) 32.8% (68.2) 48.3% 51.6%
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 97 (58) 15 (75) 99 (59) - 42 (52) - 0 (89) - - 94.3% 76.6%
RP MLB AVG 27.1% (26) 27.4% (10) 26.6% (12) 29.4% (22) 28.2% (16) 27.1% (11) 21.7% (16) 22.9% (17) 22.0% (9) 27.8% 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 6 1 21 78 1 20 20 95 9 77 29 83 92 75
RP MLB AVG 43.5% 21.7% 24.6% 10.2% 34.8% 41.0% 33.8% 25.3% 18.2% 62.7% 24.5% 5.8% 7.0% 37.0%
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 91 85 82 85 46 51 8 30 80 2 21 49 75 86
RP MLB AVG .241 .315 .289 .320 .236 .316 .280 .360 87.7 89.2 13.4 17.7% 37.0% 24.6%
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 26 48 31 42 93 9 93 97 71 77 86 95 19 70 89 78
RP MLB AVG 44.5% 63.9% 47.5% 31.9% 25.6% 18.2% 74.4% 83.9% 58.5% 16.4% 12.2% 28.5% 17.1% 58.4% 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 26 99 92 2 57 7 18 82 50 46
RP MLB AVG 44.5% 34.4% 27.1% 38.5% 36.5% 22.8% 40.7% 29.8% 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 37 40 47 11 56 64 58 13 86
RP MLB AVG 58.5% 12.1% 30.0% 14.5% 61.0% 50.2% 21.2% 26.9% 19.2%
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 40.2% 18.6% 41.2% -1.0% 5.5% -2.9 -1 3.98
RP MLB Percentile 0 12 4 69 10 10 28 70 56 27
RP MLB AVG 721 4.94 46.0% 17.4% 36.6% 9.4% 4.7% 0.7 0 3.50
Career 199 4.77 40.2% 18.6% 41.2% -1.0% 5.5% -2.9 -1 3.98
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