Joe Mack, Josh White, William Kempner selected to Marlins 40-man roster

[Ely Sussman]

It isn't very often that I'm in full agreement with the Miami Marlins on roster moves, but Tuesday was an exception. They selected catcher Joe Mack and right-handers Josh White and William Kempner to their 40-man roster, protecting them from next month's MLB Rule 5 draft. To clear a spot on the 40-man to accommodate all three prospects, outfielder Joey Wiemer was designated for assignment.

Mack has risen to No. 2 on the Fish On First Top 30 list following a season in which he represented the Marlins at the Futures Game. Spending most of 2025 at the Triple-A level, he slashed .257/.338/.475 with 21 home runs and nine stolen bases, and he played plus defense behind the plate, including a 33.3% caught stealing rate. He turns 23 next month.

White (FOF #21) has emerged as a fascinating relief arm. Another homegrown Marlins prospect, he pitched to a 1.86 ERA, 40.8 K% and .166 BAA in 45 appearances this season against AA/AAA competition. He could challenge for an Opening Day job depending on how active the team is shopping for veteran relievers this winter.

The unranked Kempner was nearly as effective as White (2.26 ERA, 33.6 K% and .162 BAA in 67.2 IP), though his lack of control upon being promoted to Jacksonville indicates that more developmental time is needed. A former San Francisco Giants farmhand, he was acquired by the Fish in January in exchange for international bonus pool money.

As for Wiemer, he was claimed off waivers by the Marlins in August. In 27 games for them, he slashed .236/.279/.436 with three homers and an 88 wRC+. He played excellent defense in right field over that small sample (4 DRS and 3 OAA). Worth noting that if Wiemer clears waivers this time around, the Marlins can outright him to the minors and maintain club control of him for the 2026 season—that's because he has never been outrighted before and does not have the seven years of professional experience needed to elect minor league free agency.

Notable Rule 5-eligible prospects who were left unprotected by the Marlins include:

• OF Andrew Pintar (acquired in the 2024 A.J. Puk trade)
• 1B Nathan Martorella (acquired in the 2024 Luis Arraez trade)
• INF/OF Jacob Berry (Miami's 2022 first-round draft pick)
• INF Yiddi Cappe (2022 Marlins Minor League Player of the Year)
• RHP Matt Pushard (career 3.21 ERA in 174 innings pitched as a minor leaguer)

 

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The Rule 5 draft will be held on December 10 in Orlando as the final event of the MLB Winter Meetings. The draft order is determined by the previous season's reverse standings, so the Marlins will pick 12th.

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[THOMAS JOSEPH]

I think we will regret the Wiemer move if he does not re-sign with the Marlins somehow.

[One Regend]

The Marlins must have a lot of faith in Andrew Nardi not only being healthy in Spring Training 2026, but to also return to form. That is a lot of misguided faith for a guy who hasn't pitched in nearly 2 years and *still* hasn't shown progress on the injury front.

[Ely Sussman]

On 11/20/2025 at 12:30 AM, One Regend said:

The Marlins must have a lot of faith in Andrew Nardi not only being healthy in Spring Training 2026, but to also return to form. That is a lot of misguided faith for a guy who hasn't pitched in nearly 2 years and *still* hasn't shown progress on the injury front.

Still a final opportunity today to cut him loose with no strings attached.

Despite coming up on arb eligibility, keep in mind Nardi has all of his minor league options left. Holding onto him through tonight's deadline just signals that he's worth a 40-man spot, not necessarily a 26-man one.