With the 2025 season wrapping up, we can begin to look back on the past five-plus months of minor league games and draw some conclusions. The sample size of data available is now standardized, allowing us to view certain metrics with a greater degree of confidence.
One such piece of data is our internal Stuff+ metric, for which we access the full suite of minor league data via sourcing and apply our proprietary formula developed by Dylan White. For today’s deep dive, we’ll be using normalized versions of these Stuff+ scores to identify some sleeper pitching prospects who popped up this season and are worth paying attention to.
We normalize our Stuff+ score results by rebalancing the data of each pitch classification against the average Stuff+ for that pitch type. In other words, because the average slider has a Stuff+ of 110, if a pitcher has a slider with a Stuff+ of 110, it is considered an “average” example of such a pitch and would therefore be rebalanced to 100 on the normalized scale. The weighted average of each pitcher’s normalized arsenal then results in their normalized Stuff+ score.
Using this model allows us to more accurately identify which pitchers are bringing elite stuff to each at-bat. And to increase our chances for identifying starters, we made sure each of the nine players included below threw a minimum of 900 pitches in the minors this season.
With all that in mind, let’s take a look at some arms who stood out as potential sleeper picks.
Christian Oppor, LHP, White Sox
The 2025 season was a big one for Oppor, as the lefthander spent all of 2024 on the complex before making his full-season debut this year.
Oppor mixes three above-average pitches, per Stuff+. His four-seam fastball sits in the mid 90s, and he mixes a changeup with good velocity and vertical separation off the heater. Oppor’s low-80s sweeper registers the highest of any pitch in his arsenal and also boasts the highest whiff rate.
Oppor was a true breakout performer for the White Sox this season.
Gerelmi Maldonado, RHP, Giants
Signed out of Venezuela in January 2021, Maldonado had Tommy John surgery in December 2023 and returned to action in 2025. Over 23 appearances this season spanning 59 innings, Maldonado flashed some of the best stuff in the minors.
At present, Maldonado works with a limited arsenal of only two pitches, hinting at a likely relief role long term. His four-seam fastball sits 97-98 mph, touching…