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William Kempner
- Jacksonville Jumbo Shrimp - AAA
- RHP
Collapse Explore Scouting Report
- Bats: R / Throws: R
- Age: 24
- Rule 5 Eligible: On 40-Man Roster
- Acquisition Method: Trade
Scouting Report
Acquired via trade from the San Francisco Giants in 2025
November 2025 update: Coming off a career year, Kempner was selected to the Marlins 40-man roster.
The thick right-hander throws from an extremely low arm angle (just a few degrees above a true sidearm delivery). He's a tough assignment for righty batters, who have to guess whether they're getting a sinker that averages 18 inches of armside run or a slider breaking 14 inches in the opposite direction. When facing lefties, the 24-year-old leans heavily on his four-seam fastball, which averaged 94.9 mph in his Triple-A appearances and topped out at 98.3 mph.
Although his 2025 campaign was impressive overall, Kempner's control eroded as the level of competition increased:
- 9.0 BB% and 3 HBP at High-A (111 batters faced)
- 15.6 BB% and 2 HBP at Double-A (96 batters faced)
- 19.7 BB% and 3 HBP at Triple-A (76 batters faced)
Kempner has three minor league options remaining entering 2026.
Monthly Splits
| Split | Team | W | L | ERA | G | GS | CG | SHO | SV | SVO | IP | H | R | ER | HR | HB | BB | IBB | SO | AVG | WHIP | GO/AO |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| No Outs | -- | -- | -- | 21 | -- | -- | -- | -- | -- | 9.1 | 3 | -- | -- | 1 | 1 | 5 | 0 | 14 | .100 | 0.86 | 0.30 | |
| Two Outs | -- | -- | -- | 23 | -- | -- | -- | -- | -- | 11.0 | 9 | -- | -- | 1 | 2 | 6 | 1 | 20 | .214 | 1.36 | 1.17 | |
| One Out | -- | -- | -- | 23 | -- | -- | -- | -- | -- | 10.0 | 6 | -- | -- | 1 | 0 | 5 | 0 | 17 | .176 | 1.10 | 0.30 | |
| Ahead in Count | -- | -- | -- | 23 | -- | -- | -- | -- | -- | 13.2 | 6 | -- | -- | 1 | 0 | 0 | 0 | 26 | .130 | 0.44 | 0.67 | |
| Runners at 1st & 2nd | JAX | -- | -- | -- | 7 | -- | -- | -- | -- | -- | 2.1 | 1 | -- | -- | 0 | 0 | 1 | 0 | 5 | .125 | 0.86 | 0.00 |
| Batting Seventh | -- | -- | -- | 17 | -- | -- | -- | -- | -- | 4.1 | 2 | -- | -- | 0 | 0 | 2 | 0 | 8 | .133 | 0.92 | 0.25 | |
| Runners at 1st & 3rd | -- | -- | -- | 3 | -- | -- | -- | -- | -- | 0.2 | 0 | -- | -- | 0 | 0 | 0 | 0 | 1 | .000 | 0.00 | 0.00 | |
| Batting Sixth | -- | -- | -- | 15 | -- | -- | -- | -- | -- | 3.1 | 3 | -- | -- | 0 | 0 | 2 | 0 | 6 | .231 | 1.50 | 1.00 | |
| Batting Ninth | -- | -- | -- | 17 | -- | -- | -- | -- | -- | 3.2 | 3 | -- | -- | 2 | 1 | 3 | 0 | 7 | .214 | 1.64 | 1.00 | |
| Bases Loaded | -- | -- | -- | 3 | -- | -- | -- | -- | -- | 1.1 | 0 | -- | -- | 0 | 0 | 1 | 0 | 3 | .000 | 0.75 | 1.00 | |
| Batting Eighth | -- | -- | -- | 18 | -- | -- | -- | -- | -- | 3.2 | 2 | -- | -- | 0 | 1 | 4 | 1 | 6 | .154 | 1.64 | 0.67 | |
| On Grass | 0 | 3 | 4.18 | 21 | 0 | 0 | 0 | 5 | 6 | 28.0 | 17 | 14 | 13 | 3 | 3 | 16 | 1 | 49 | .173 | 1.18 | 0.48 | |
| Day Games | 0 | 2 | 6.00 | 10 | 0 | 0 | 0 | 3 | 4 | 12.0 | 11 | 9 | 8 | 3 | 2 | 4 | 0 | 19 | .250 | 1.25 | 0.45 | |
| Extra Innings | JAX | -- | -- | 0.00 | 1 | -- | -- | -- | -- | -- | 1.0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 1 | .000 | 0.00 | 1.00 |
| Home Games | 0 | 0 | 3.55 | 11 | 0 | 0 | 0 | 4 | 4 | 12.2 | 7 | 5 | 5 | 1 | 1 | 8 | 0 | 24 | .159 | 1.18 | 0.75 | |
| Away Games | 0 | 3 | 4.08 | 12 | 0 | 0 | 0 | 1 | 2 | 17.2 | 11 | 9 | 8 | 2 | 2 | 8 | 1 | 27 | .177 | 1.08 | 0.39 | |
| Pre All-Star | MIA | 0 | 0 | 0.00 | 4 | 0 | 0 | 0 | 0 | 0 | 4.2 | 3 | 0 | 0 | 0 | 0 | 0 | 0 | 5 | .176 | 0.64 | 0.80 |
| Seventh Inning | -- | -- | 1.13 | 10 | -- | -- | -- | -- | -- | 8.0 | 5 | 1 | 1 | 0 | 1 | 4 | 0 | 18 | .172 | 1.13 | 0.50 | |
| Behind in Count | -- | -- | -- | 22 | -- | -- | -- | -- | -- | 6.0 | 6 | -- | -- | 1 | 2 | 16 | 1 | 10 | .250 | 3.67 | 0.60 | |
| Runner at 3rd | JAX | -- | -- | -- | 3 | -- | -- | -- | -- | -- | 0.2 | 0 | -- | -- | 0 | 0 | 1 | 1 | 1 | .000 | 1.50 | 0.00 |
| June | MIA | 0 | 0 | 0.00 | 1 | 0 | 0 | 0 | 0 | 0 | 1.1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | .200 | 0.75 | 0.50 |
| Eighth Inning | -- | -- | 5.40 | 10 | -- | -- | -- | -- | -- | 8.1 | 4 | 5 | 5 | 1 | 1 | 6 | 1 | 10 | .138 | 1.20 | 0.50 | |
| Runner at 2nd | JAX | -- | -- | -- | 7 | -- | -- | -- | -- | -- | 1.0 | 2 | -- | -- | 1 | 1 | 1 | 0 | 2 | .400 | 3.00 | 1.00 |
| May | 0 | 0 | 1.15 | 11 | 0 | 0 | 0 | 2 | 2 | 15.2 | 4 | 3 | 2 | 0 | 1 | 5 | 0 | 18 | .080 | 0.57 | 0.53 | |
| Leading Off Inning | -- | -- | -- | 21 | -- | -- | -- | -- | -- | 7.1 | 2 | -- | -- | 1 | 1 | 3 | 0 | 10 | .083 | 0.68 | 0.33 | |
| Ninth Inning | JAX | -- | -- | 2.16 | 9 | -- | -- | -- | -- | -- | 8.1 | 4 | 2 | 2 | 0 | 1 | 4 | 0 | 16 | .143 | 0.96 | 0.50 |
| On Turf | MIA | 0 | 0 | 0.00 | 2 | 0 | 0 | 0 | 0 | 0 | 2.1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | .125 | 0.43 | 0.67 |
| Scoring Position | -- | -- | -- | 12 | -- | -- | -- | -- | -- | 6.0 | 5 | -- | -- | 1 | 1 | 5 | 1 | 12 | .238 | 1.67 | 0.50 | |
| April | JAX | 0 | 3 | 8.25 | 9 | 0 | 0 | 0 | 2 | 3 | 12.0 | 12 | 11 | 11 | 3 | 2 | 10 | 1 | 28 | .261 | 1.83 | 0.40 |
| Runners at 2nd & 3rd | JAX | -- | -- | -- | 3 | -- | -- | -- | -- | -- | 0.0 | 2 | -- | -- | 0 | 0 | 1 | 0 | 0 | 1.000 | -.-- | -.-- |
| vs Right | -- | -- | -- | 22 | -- | -- | -- | -- | -- | 15.0 | 11 | -- | -- | 1 | 1 | 10 | 1 | 23 | .196 | 1.40 | 0.57 | |
| Runner at 1st | -- | -- | -- | 15 | -- | -- | -- | -- | -- | 6.1 | 4 | -- | -- | 1 | 0 | 4 | 0 | 12 | .182 | 1.26 | 0.50 | |
| Reliever | 0 | 3 | 3.86 | 23 | 0 | 0 | 0 | 5 | 6 | 30.1 | 18 | 14 | 13 | 3 | 3 | 16 | 1 | 51 | .170 | 1.12 | 0.50 | |
| Sixth Inning | -- | -- | 9.64 | 6 | -- | -- | -- | -- | -- | 4.2 | 5 | 5 | 5 | 2 | 0 | 2 | 0 | 6 | .278 | 1.50 | 0.40 | |
| Bases Empty | -- | -- | -- | 21 | -- | -- | -- | -- | -- | 18.0 | 9 | -- | -- | 1 | 2 | 7 | 0 | 27 | .143 | 0.89 | 0.50 | |
| Night Games | 0 | 1 | 2.45 | 13 | 0 | 0 | 0 | 2 | 2 | 18.1 | 7 | 5 | 5 | 0 | 1 | 12 | 1 | 32 | .113 | 1.04 | 0.53 | |
| March | JAX | 0 | 0 | 0.00 | 2 | 0 | 0 | 0 | 1 | 1 | 1.1 | 1 | 0 | 0 | 0 | 0 | 1 | 0 | 4 | .200 | 1.50 | -.-- |
| Late / Close | -- | -- | -- | 7 | -- | -- | -- | -- | -- | 5.0 | 6 | -- | -- | 1 | 0 | 7 | 1 | 12 | .286 | 2.60 | 0.50 | |
| vs Left | -- | -- | -- | 20 | -- | -- | -- | -- | -- | 15.0 | 7 | -- | -- | 2 | 2 | 6 | 0 | 28 | .140 | 0.87 | 0.42 | |
| Batting Third | -- | -- | -- | 10 | -- | -- | -- | -- | -- | 2.1 | 1 | -- | -- | 0 | 0 | 2 | 0 | 1 | .125 | 1.29 | 0.50 | |
| Batting Second | -- | -- | -- | 10 | -- | -- | -- | -- | -- | 2.0 | 3 | -- | -- | 0 | 1 | 0 | 0 | 5 | .333 | 1.50 | 0.00 | |
| Batting Fifth | -- | -- | -- | 12 | -- | -- | -- | -- | -- | 3.1 | 1 | -- | -- | 0 | 0 | 1 | 0 | 5 | .100 | 0.60 | 0.25 | |
| Batting Fourth | JAX | -- | -- | -- | 13 | -- | -- | -- | -- | -- | 3.2 | 2 | -- | -- | 1 | 0 | 0 | 0 | 8 | .154 | 0.55 | 0.00 |
| Batting First | -- | -- | -- | 14 | -- | -- | -- | -- | -- | 3.2 | 1 | -- | -- | 0 | 0 | 2 | 0 | 5 | .091 | 0.82 | 1.00 | |
| First Half | JAX | 0 | 3 | 4.56 | 19 | 0 | 0 | 0 | 5 | 6 | 25.2 | 15 | 14 | 13 | 3 | 3 | 16 | 1 | 46 | .169 | 1.21 | 0.43 |
| Season | Team | LG | Level | W | L | ERA | G | GS | CG | SHO | HLD | SV | SVO | IP | H | R | ER | HR | NP | HB | BB | IBB | SO | AVG | WHIP | GO/AO |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 2022 | 2 teams | - | Minors | 1 | 0 | 5.00 | 5 | 2 | 0 | 0 | 0 | 0 | 0 | 9.0 | 10 | 5 | 5 | 1 | 140 | 2 | 6 | 0 | 11 | .294 | 1.78 | 1.33 |
| 2022 | A-GIB | ACL | ROK | 1 | 0 | 2.70 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 3.1 | 4 | 1 | 1 | 0 | 32 | 0 | 2 | 0 | 5 | .333 | 1.80 | 4.00 |
| 2022 | SJ | CAL | A | 0 | 0 | 6.35 | 3 | 2 | 0 | 0 | 0 | 0 | 0 | 5.2 | 6 | 4 | 4 | 1 | 108 | 2 | 4 | 0 | 6 | .273 | 1.76 | 0.67 |
| 2023 | 3 teams | - | Minors | 4 | 5 | 3.73 | 38 | 5 | 0 | 0 | 3 | 1 | 4 | 62.2 | 52 | 34 | 26 | 5 | 1104 | 10 | 30 | 0 | 78 | .222 | 1.31 | 1.08 |
| 2023 | SJ | CAL | A | 1 | 3 | 4.67 | 14 | 5 | 0 | 0 | 1 | 1 | 1 | 27.0 | 21 | 18 | 14 | 0 | 462 | 5 | 15 | 0 | 29 | .208 | 1.33 | 1.26 |
| 2023 | EUG | NWL | A+ | 3 | 2 | 2.91 | 23 | 0 | 0 | 0 | 2 | 0 | 3 | 34.0 | 28 | 15 | 11 | 5 | 600 | 5 | 13 | 0 | 47 | .224 | 1.21 | 0.96 |
| 2023 | RIC | EAS | AA | 0 | 0 | 5.40 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1.2 | 3 | 1 | 1 | 0 | 42 | 0 | 2 | 0 | 2 | .375 | 3.00 | 0.50 |
| 2025 | 3 teams | - | Minors | 7 | 3 | 2.26 | 48 | 0 | 0 | 0 | 1 | 7 | 7 | 67.2 | 38 | 20 | 17 | 2 | 1217 | 8 | 40 | 0 | 95 | .162 | 1.15 | 1.08 |
| 2025 | BEL | MID | A+ | 1 | 2 | 3.04 | 19 | 0 | 0 | 0 | 0 | 6 | 6 | 26.2 | 19 | 11 | 9 | 0 | 452 | 3 | 10 | 0 | 39 | .196 | 1.09 | 1.67 |
| 2025 | PNS | SOU | AA | 3 | 1 | 1.13 | 16 | 0 | 0 | 0 | 1 | 0 | 0 | 24.0 | 11 | 4 | 3 | 0 | 412 | 2 | 15 | 0 | 31 | .139 | 1.08 | 0.85 |
| 2025 | JAX | INT | AAA | 3 | 0 | 2.65 | 13 | 0 | 0 | 0 | 0 | 1 | 1 | 17.0 | 8 | 5 | 5 | 2 | 353 | 3 | 15 | 0 | 25 | .138 | 1.35 | 0.79 |
| 2026 | JAX | INT | AAA | 0 | 3 | 4.56 | 19 | 0 | 0 | 0 | 2 | 5 | 6 | 25.2 | 15 | 14 | 13 | 3 | 481 | 3 | 16 | 1 | 46 | .169 | 1.21 | 0.43 |
| Date | Team | OPP | W | L | ERA | G | GS | CG | SHO | SV | SVO | IP | H | R | ER | HR | HB | BB | IBB | SO | AVG | WHIP | GO/AO |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 2026-03-27 | JAX | vs ROC | 0 | 0 | 0.00 | 1 | 0 | 0 | 0 | 0 | 0 | 0.2 | 1 | 0 | 0 | 0 | 0 | 1 | 0 | 2 | .333 | 3.00 | -.-- |
| 2026-03-29 | JAX | vs ROC | 0 | 0 | 0.00 | 1 | 0 | 0 | 0 | 1 | 1 | 0.2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | .200 | 1.50 | -.-- |
| 2026-04-01 | JAX | vs SUG | 0 | 0 | 6.75 | 1 | 0 | 0 | 0 | 0 | 0 | 1.1 | 2 | 2 | 2 | 1 | 0 | 0 | 0 | 4 | .273 | 1.50 | -.-- |
| 2026-04-04 | JAX | vs SUG | 0 | 0 | 4.50 | 1 | 0 | 0 | 0 | 1 | 1 | 1.1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | .200 | 1.00 | 1.00 |
| 2026-04-07 | JAX | @ NOR | 0 | 0 | 3.00 | 1 | 0 | 0 | 0 | 0 | 0 | 2.0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 4 | .143 | 0.83 | 2.00 |
| 2026-04-10 | JAX | @ NOR | 0 | 1 | 5.14 | 1 | 0 | 0 | 0 | 0 | 0 | 1.0 | 0 | 2 | 2 | 0 | 0 | 4 | 1 | 3 | .125 | 1.29 | 2.00 |
| 2026-04-16 | JAX | vs CLT | 0 | 0 | 4.50 | 1 | 0 | 0 | 0 | 1 | 1 | 1.0 | 1 | 0 | 0 | 0 | 0 | 2 | 0 | 3 | .143 | 1.50 | 2.00 |
| 2026-04-19 | JAX | vs CLT | 0 | 0 | 5.00 | 1 | 0 | 0 | 0 | 0 | 0 | 1.0 | 0 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | .133 | 1.44 | 0.67 |
| 2026-04-22 | JAX | @ GWN | 0 | 1 | 7.45 | 1 | 0 | 0 | 0 | 0 | 1 | 0.2 | 3 | 3 | 3 | 1 | 0 | 2 | 0 | 1 | .200 | 1.86 | 0.50 |
| 2026-04-24 | JAX | @ GWN | 0 | 0 | 7.15 | 1 | 0 | 0 | 0 | 0 | 0 | 1.2 | 2 | 1 | 1 | 0 | 0 | 0 | 0 | 4 | .214 | 1.76 | 0.40 |
| 2026-04-28 | JAX | @ DUR | 0 | 1 | 7.43 | 1 | 0 | 0 | 0 | 0 | 0 | 2.0 | 4 | 2 | 2 | 1 | 1 | 0 | 0 | 5 | .255 | 1.80 | 0.40 |
| 2026-05-01 | JAX | @ DUR | 0 | 0 | 6.46 | 1 | 0 | 0 | 0 | 0 | 0 | 2.0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | .228 | 1.57 | 0.38 |
| 2026-05-05 | MIA | vs BAL | 0 | 0 | 0.00 | 1 | 0 | 0 | 0 | 0 | 0 | 1.0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | .000 | 0.00 | 1.00 |
| 2026-05-08 | JAX | vs CLT | 0 | 0 | 5.71 | 1 | 0 | 0 | 0 | 0 | 0 | 2.0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 3 | .206 | 1.44 | 0.56 |
| 2026-05-12 | JAX | @ MEM | 0 | 0 | 5.12 | 1 | 0 | 0 | 0 | 0 | 0 | 2.0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | .188 | 1.29 | 0.46 |
| 2026-05-14 | JAX | @ MEM | 0 | 0 | 4.87 | 1 | 0 | 0 | 0 | 1 | 1 | 1.0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 1 | .183 | 1.23 | 0.50 |
| 2026-05-17 | JAX | @ MEM | 0 | 0 | 4.43 | 1 | 0 | 0 | 0 | 0 | 0 | 2.0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 1 | .169 | 1.16 | 0.44 |
| 2026-05-20 | JAX | vs NOR | 0 | 0 | 4.24 | 1 | 0 | 0 | 0 | 1 | 1 | 1.0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | .163 | 1.11 | 0.47 |
| 2026-05-22 | JAX | vs NOR | 0 | 0 | 4.74 | 1 | 0 | 0 | 0 | 0 | 0 | 1.1 | 2 | 2 | 2 | 0 | 0 | 3 | 0 | 3 | .174 | 1.26 | 0.45 |
| 2026-05-26 | JAX | @ CLT | 0 | 0 | 4.56 | 1 | 0 | 0 | 0 | 0 | 0 | 1.0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | .169 | 1.21 | 0.43 |
| 2026-05-30 | MIA | @ NYM | 0 | 0 | 0.00 | 1 | 0 | 0 | 0 | 0 | 0 | 1.0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | .000 | 0.00 | 1.50 |
| 2026-05-31 | MIA | @ NYM | 0 | 0 | 0.00 | 1 | 0 | 0 | 0 | 0 | 0 | 1.1 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | .167 | 0.60 | 1.00 |
| 2026-06-05 | MIA | vs TB | 0 | 0 | 0.00 | 1 | 0 | 0 | 0 | 0 | 0 | 1.1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | .176 | 0.64 | 0.80 |
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