William Kempner

RP · R/R · age 25.2 · MIA

60-DAY ILOCTOBER: REINSTATE

Roster status
60-DAY IL (Elbow surgery)
Service thru 2025
0+000
Service now / projected
0+092 / 0+105
Option years left (2026)
3 (using one in 2026)
Assignments left this season
3 of 5
Contract (2027)
PRE-ARBITRATION / AUTO-RENEWAL
Acquired
Trade (SFG) Jan'24
Outrighted / DFA'd before
0 / 0
Contract
none listed

Next 90 days, by the model

Stays put
87%
Designated
5%
Optioned
6%
Traded
1%
Released or non-tendered
<1%

Pushing the cut risk around: roster status (2) raises it, this season's WAR (0.08) raises it, this season's strikeout rate (0.28) lowers it.

Context the model does not weigh: ZiPS projects -0.4 WAR, 0.1 WAR this season; 17 RP on the 40-man, of whom Peter Fairbanks is headed to free agency.

Trained on every 40-man roster snapshot since 2011 and what happened in the following 90 days; it sees roster status, options, service, history and last season's line, not this season's performance or the club's intentions. How well it does.

Is there a job for him next year?

MIA returns 16 RP on the 40-man once 1 free agent leaves; about 9 RP jobs survive a normal winter. By his own recent record he ranks 10th among the returners (0.2 WAR against a bar of 0.2), which the calibrated model turns into 88% kept through the tender deadline. Ranked by ZiPS and Steamer instead, which credit his longer track record, he is 16th (-0.3 WAR, bar -0.0), worth 82% kept on the same model.

By recent record: returning RPProj. WAR
1. Anthony Bender1.6
2. Ronny Henriquez1.3
3. Calvin Faucher1.3
4. Michael Petersen1.3
5. Dax Fulton0.5
6. Victor Vodnik0.5
7. Wilkelman Gonzalez0.5
8. Andrew Nardi0.3
9. Cade Gibsonlast job0.2
10. William Kempner0.2
11. Jack Ralston0.1
12. Josh Ekness-0.4
By ZiPS / Steamer: returning RPProj. WAR
1. Ronny Henriquez0.5
2. Andrew Nardi0.4
3. Dax Fulton0.3
4. Josh White0.3
5. Anthony Bender0.2
6. Victor Vodnik0.2
7. Calvin Faucher0.2
8. Cade Gibson0.0
9. Michael Petersenlast job-0.0
10. Tyler Zuber-0.1
11. Josh Ekness-0.1
12. Jack Ralston-0.1

Departing free agents are excluded; players on club, mutual or player options are counted as returning. The kept probability is calibrated on every September since 2012 using the recent-record projection; the ZiPS/Steamer reading uses the same model with a different ranking, so treat it as a second opinion rather than a calibrated number. Salary enters once arbitration projections publish in October.

October: Eligible once reinstated

On the 60-day IL before the cutoff, so he is on the eligibility list. He has served the 60 days (64), so the only step is reinstatement: the club must open a 40-man spot and a 26-man spot before the series roster is submitted.

The post-season eligibility list is fixed at noon ET on September 1: everyone on the 40-man, the 60-day IL or the military list at that moment, who then stays there without interruption. Attachment 25 (Major League Rule 40)

What happens if the club…

option him to the minorsBLOCKED
Not while he is on the injured list. He must be healthy and reinstated first; a rehab assignment (20 days, 30 for pitchers, with his consent) is the only way to send him down injured.
Injured players cannot be sent down
designate him for assignment (or put him on outright waivers)
The club has 7 days to trade him, pass him through outright waivers, or release him; he is paid at the major-league rate and keeps accruing service in the meantime. On outright waivers any club can claim him for $50,000, worst record first, and the claiming club takes his contract. If he clears, the club can outright him to the minors and he has no say; he stays under club control on a minor-league deal. He would then be Rule 5-eligible and would hold XX-D rights against any future outright. Post-season: an outright after the September 1 cutoff ends his automatic eligibility. He could only return as an approved injury replacement, and only if he accepts the outright and stays on a minor-league reserve list in the organization without interruption; a release makes him ineligible for anyone this October. Because he is on the injured list he cannot be outrighted until he is healthy and reinstated, so a DFA now would have to end in a trade or a release.
Designated for assignment: 7 days · Outright waivers · Article XX-D: the right to walk
release him
Release waivers cost a claiming club $1 but the claimant assumes the whole contract, so expensive players clear. The club owes the full unpaid balance of this season's salary, offset by whatever another club pays him this year. A released player is not post-season eligible for any club this year.
Release waivers and termination pay · Which rate a split contract pays at release
trade himBLOCKED
Not now: players on major-league contracts cannot be traded after the Aug 3 deadline until the day after the World Series.
Trade deadline · 10-and-5 rights · June 15 no-trade for free-agent signees
renew him for next year
Pre-arbitration: the club sets his 2027 salary near the minimum ($780,000 floor) and he has no leverage beyond a non-tender.
Minimum salaries · Tender deadline

What the rules say about him

Option years, season by season

SeasonDays on optionOption year usedStints
202682yesMar 8, 2026 to May 5, 2026 (41d, spring training)May 6, 2026 to May 30, 2026 (24d)Jun 16, 2026 to Jul 3, 2026 (17d)

Transaction log

Aug 21, 2026Status changeMiami Marlins transferred RHP William Kempner from the 15-day injured list to the 60-day injured list. Right elbow sprain.
Jul 12, 2026Status changeMiami Marlins placed RHP William Kempner on the 15-day injured list. Right elbow sprain.
Jul 3, 2026RecalledMiami Marlins recalled RHP William Kempner from Jacksonville Jumbo Shrimp.
Jun 16, 2026OptionedMiami Marlins optioned RHP William Kempner to Jacksonville Jumbo Shrimp.
May 30, 2026RecalledMiami Marlins recalled RHP William Kempner from Jacksonville Jumbo Shrimp.
May 6, 2026OptionedMiami Marlins optioned RHP William Kempner to Jacksonville Jumbo Shrimp.
May 5, 2026RecalledMiami Marlins recalled RHP William Kempner from Jacksonville Jumbo Shrimp.
Mar 8, 2026OptionedMiami Marlins optioned RHP William Kempner to Jacksonville Jumbo Shrimp.
Nov 18, 2025Contract selectedMiami Marlins selected the contract of RHP William Kempner from Jacksonville Jumbo Shrimp.
Jan 15, 2025TradedSan Francisco Giants traded RHP William Kempner to Miami Marlins for Future Considerations. International Bonus Pool Money.
Jul 28, 2022SignedSan Francisco Giants signed RHP William Kempner.

Service through 2025 per FanGraphs RosterResource; options and this-season service reconstructed from the MLB transaction log (reconstruction; FanGraphs shows 3). Rule 5 exposure deadline Nov 17, 2026.