Players · K · Pitcher · 2026 regular season
William Kempner
- Age
- 25
- B/T
- R/R
- Height
- 6' 0"
- Weight
- 222 lb
- Number
- #71
- Born
- June 18, 2001 in San Jose, CA, United States
- MLB debut
- May 5, 2026
- Drafted
- 2022, round 3
- College
- Gonzaga
- High school
- Valley Christian
- dbWAR
- .2 Regular season, 1 season(s)
- IP
- 12.1
- ERA
- 2.92
- FIP
- 3.35
- K/9
- 10.2
- FIP−
- 80 100 = avg
William Kempner is a relief pitcher for the Miami Marlins. In 2026 he struck out 14 batters over 12.1 innings across 9 appearances, going 1-0. His ERA of 2.92 was 30.2% lower than the league average of 4.18. Stripping out defence, his 3.35 FIP suggests that his ERA had some help behind him. He missed bats on 34.1% of swings (15.6% of every pitch he threw), walked 8.0% of the batters he faced and struck out 28.0%. His 0.2 dbWAR is built from that FIP rather than runs allowed, so it credits him for what he controls and not for the defence behind him.
League context
Percentile among qualified pitchers, 2026 regular season.
Pitching Regular season
Standard and advanced, by season. Regular-season games only.
| Trend | ||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 2026 | MIA | 9 | 0 | 12.1 | 1 | 0 | 0 | 8 | 4 | 14 | 4 | 2.92 | 3.35 | 0.97 | 10.2 | 2.9 | 70 | 80 | 0.2 | — |
Platoon splits
How left- and right-handed hitters fare against him.
| Split | PA | AB | H | HR | BB | SO | AVG | OBP | SLG | wOBA | K% |
|---|---|---|---|---|---|---|---|---|---|---|---|
| vs LHB | 33 | 30 | 5 | 1 | 2 | 12 | .167 | .242 | .333 | .258 | 36.4% |
| vs RHB | 17 | 14 | 3 | 0 | 2 | 2 | .214 | .353 | .214 | .287 | 11.8% |
Pitch sequencing
What William Kempner throws in each count, and what he follows each pitch with. Select any cell for the breakdown.
Select a count to see exactly what William Kempner throws in it.
Pitch arsenal
What he throws, how hard, how often it misses, and what hitters do with it.
| Four-Seam Fastball | 96 | 95.5 | 2,395 | 53.1% | 39.0% | 19 | .316 | 1.037 | |
| Sweeper | 44 | 81.6 | 2,905 | 45.5% | 32.1% | 13 | — | — | |
| Sinker | 29 | 94.0 | 2,251 | 31.0% | 18.2% | 8 | — | — | |
| Cutter | 25 | 87.3 | 2,623 | 64.0% | 44.4% | 3 | — | — |
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wOBA uses linear weights measured from this season's own play-by-play rather than published constants, and wRC+ is park-adjusted against that same league. dbWAR is our own open implementation — not fWAR or bWAR — and the full derivation, including its simplifications, is on the methodology page.