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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 1.0 0.00 0.00 33.3% 0.0%
111th 1
Sv
357th 13.0
IP
1st 4.93
ERA
1st 1.48
WHIP
25th 22.1%
K%
1st 10.7%
BB%
FB MPH SwStr% CSW% Str-ICR MTK% PLV PLA
97.6 12.5% 37.5% - 12.5% 4.26 3.28
26th 94.0
FB MPH
150th 11.8%
SwStr%
7th 28.4%
CSW%
- 49.9%
Str-ICR
356th 4.7%
MTK%
356th 4.90
PLV
160th 3.83
PLA
Holds List
Rank
119th

Articles

5/6/2026Fantasy Baseball Relief Pitcher Roundup: 5/5Rick Graham

5/6/2026Relief Pitcher Streamer Rankings Fantasy Baseball: 5/6Rick Graham

3/13/2026Top 300 Relievers for Fantasy Baseball 2026 - UPDATEDRick 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 1 0 1.0 0-0 0 0 0.00 0.00 0.15 1.14 1.14 3.28 33.3% 0.0% 0.0 0.00 .000 - - - 50.0% 12.5% 37.5% 0.75 4.26
RP MLB Percentile 0 0 0 0-49 0 0 96 100 100 97 99 55 92 97 99 73 99 - - - 66 57 98 96 0
RP MLB AVG 10 0 13.0 1-1 1 2 4.93 1.48 4.61 4.62 4.50 3.83 22.1% 10.7% 8.9 1.19 .302 18.7% 71.3% 38.1% 44.0% 11.8% 28.4% 0.48 4.90
Career 1 0 1.0 0-0 0 0 0.00 0.00 0.15 1.14 1.14 3.28 33.3% 0.0% 0.0 0.00 .000 - - - 50.0% 12.5% 37.5% 0.75 4.26

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 1 0 1.0 0-0 0 0 0 8 6 2 3 0 0 0 0 0 1 0 0 0
RP MLB Percentile 0 0 0 0-49 0 0 0 0 0 100 0 99 98 82 16 73 1 97 45 39
RP MLB AVG 10 0 13.0 1-1 0 1 2 229 144 85 58 13 8 2 0 2 13 6 1 1
Career 1 0 1.0 0-0 0 0 0 8 6 2 3 0 0 0 0 0 1 0 0 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 33.3% 0.0% .000 .000 .000 .000 .000 .000 .056 .061 .084 .091 91.5 - 29.5 0.15
RP MLB Percentile 92 97 99 99 100 100 99 99 100 100 99 99 15 - 1 100
RP MLB AVG 22.1% 10.7% .251 .406 .744 .331 .302 .332 .242 .330 .287 .373 88.2 89.5 13.1 4.61
Career 33.3% 0.0% .000 .000 .000 .000 .000 .000 .056 .061 .084 .091 91.5 - 29.5 0.15

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 62.5% (97.6) - - - 37.5% (83.8) - - - - 62.5% 37.5%
RP MLB Percentile 94 (92) - - - 85 (66) - - - - 87.7% 12.6%
RP MLB AVG 34.9% (94.0) 26.9% (93.9) 21.1% (89.2) 27.2% (85.6) 23.2% (82.5) 17.8% (80.8) 18.5% (86.1) 19.1% (86.3) 35.9% (68.2) 47.4% 52.4%
Career 62.5% (97.6) - - - 37.5% (-) - - - - 62.5% 37.5%

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 60.0% (1) - - - 0.0% (0) - - - - 60.0% 0.0%
RP MLB Percentile 99 (74) - - - 0 (0) - - - - 98.9% 0.0%
RP MLB AVG 26.4% (7) 28.4% (4) 28.3% (5) 30.2% (8) 28.4% (7) 27.6% (5) 22.0% (6) 25.7% (8) 21.4% (5) 27.9% 28.3%
Career 60.0% (1) - - - 0.0% (0) - - - - 60.0% 0.0%

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 50.0% 0.0% 0.0% 50.0% 0.0% 50.0% 0.0% 50.0% 12.5% 100.0% 0.0% 0.0% 0.0% -
RP MLB Percentile 66 99 0 100 100 79 0 99 8 99 98 83 88 -
RP MLB AVG 44.0% 21.7% 24.2% 10.1% 34.6% 42.0% 33.3% 24.7% 17.5% 61.8% 24.5% 6.1% 7.7% 38.1%
Career 50.0% 0.0% 0.0% 50.0% 0.0% 50.0% 0.0% 50.0% 12.5% 100.0% 0.0% 0.0% 0.0% -

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 .000 .000 .000 .000 .056 .061 .084 .091 91.5 - 29.5 - - -
RP MLB Percentile 99 100 99 99 100 100 99 99 15 - 1 - - -
RP MLB AVG .251 .331 .302 .332 .242 .330 .287 .373 88.2 89.5 13.1 18.7% 38.1% 25.1%
Career .000 .000 .000 .000 .056 .061 .084 .091 91.5 - 29.5 - - -

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 50.0% 75.0% 50.0% 25.0% 25.0% 12.5% 75.0% 100.0% 0.0% 25.0% 12.5% 37.5% 25.0% 75.0% 0.75 -
RP MLB Percentile 89 99 78 15 45 8 45 0 100 99 57 98 97 100 96 -
RP MLB AVG 44.1% 62.9% 46.3% 30.6% 25.4% 17.5% 74.6% 83.9% 59.0% 16.6% 11.8% 28.4% 17.0% 57.3% 0.48 49.9%
Career 50.0% 75.0% 50.0% 25.0% 25.0% 12.5% 75.0% 100.0% 0.0% 25.0% 12.5% 37.5% 25.0% 75.0% 0.75 -

William Kempner Approach › Locations

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Year Team Zone% aLoc% x-mLoc% gLoc% hiLoc% y-mLoc% loLoc% iLoc% oLoc% mmLoc%
2026 MIA 50.0% 37.5% 25.0% 37.5% 50.0% 0.0% 50.0% 37.5% 37.5% 0.0%
RP MLB Percentile 89 64 64 44 93 100 83 87 19 0
RP MLB AVG 44.1% 35.1% 26.6% 38.3% 36.0% 22.8% 41.1% 30.6% 42.8% 6.4%
Career 50.0% 37.5% 25.0% 37.5% 50.0% 0.0% 50.0% 37.5% 37.5% 0.0%

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 62.5% 0.0% 37.5% 40.0% 66.7% 33.3% 40.0% 33.3% 33.3%
RP MLB Percentile 86 100 97 99 81 4 100 82 95
RP MLB AVG 58.5% 13.0% 29.2% 14.1% 59.5% 49.3% 21.0% 26.1% 19.5%
Career 62.5% 0.0% 37.5% 40.0% 66.7% 33.3% 40.0% 33.3% 33.3%

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 8 4.26 0.0% 50.0% 50.0% -50.0% 12.5% -0.9 0 3.28
RP MLB Percentile 0 0 0 99 1 1 0 76 72 55
RP MLB AVG 229 4.90 44.3% 18.4% 37.3% 7.1% 4.7% 1.8 +2 3.83
Career 8 4.26 0.0% 50.0% 50.0% -50.0% 12.5% -0.9 0 3.28
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