Developing Major League prospects is a long game. But teams like the Miami Marlins only get to hang onto them for so long.
MLB rules require teams to make decisions on prospects by a deadline. For players signed before age 18 it’s five years. For any player signed after age 19 its four years. At that point, those players must either be placed on the 40-man roster or be left exposed to the Rule 5 draft, which is in December at MLB’s winter meetings.
The Rule 5 draft allows teams to select players that fit the criteria. Teams that possess top prospects must make decisions on the future of these prospects before Tuesday’s 6 p.m. eastern deadline. No player is more top of mind for the Marlins than catching prospect Joe Mack.
Joe Mack’s Miami Future
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Mack, the No. 70 prospect in the Majors per MLB Pipeline, falls into the first category. He was signed at 18 years old when the Marlins took him in the first round of the 2021 MLB draft out of Williamsville East High School in Williamsville, N.Y. He has quietly, but steadily, made his way through the Marlins’ minor league system. He ended this season at Triple-A Jacksonville.
He has a career slash of .239/.332/.400 with 57 home runs and 189 RBI. His power numbers have gone up the last two seasons and at the higher reaches of the system. In 2024 with High-A Beloit and Double-A Pensacola he hit 24 home runs. In 2025 with Pensacola and Jacksonville he hit 21 home runs. He played the bulk of the season at Jacksonville.
Mack is coming into his own at a key moment for the Marlins. AgustÃn RamÃrez started more games behind the plate for Miami than any other player in 2025.  He slashed .231/.287/.413 with 21 home runs and 67 RBI. That’s quality power from a young catcher. But his defensive numbers were below average per FanGraphs and Statcast — minus-5 in throwing value, minus-7 in blocking value and minus-12 in fielding run value. He was minus-14 in defensive runs saved.
Mack would give the Marlins another option behind the plate. The only other catcher on the 40-man roster is Liam Hicks, also a rookie, who played in 119 games last season. Protecting Mack from the Rule 5 draft gives the Marlins plenty of young options behind the plate to either play or use in trade with another team.
The Marlins have a little space to maneuver. After some minor moves after the end of the World Series, Miami has 38 players on the 40-man roster. So, the Marlins have the space to protect him. They must decide if leaving him unprotected is worth the gamble, consider many teams need catching this offseason.
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