RJ Petit's Arsenal Explains Why Rockies Selected Him in Rule 5 Draft

The Rockies' newest 6-foot-8 flamethrower has a slider that's turning heads, and his arsenal might be exactly what Colorado needs.

Detroit Tigers right handed pitching prospect RJ Petit throws during minor-league minicamp Sunday, Feb. 20, 2022, at TigerTown in Lakeland, Florida. Tigers4 / Kirthmon F. Dozier / USA TODAY NETWORK

The Colorado Rockies selected RJ Petit with the first overall pick in the 2025 Rule 5 Draft earlier this week. The 6-foot-8, 300-pound right-hander from Detroit brings a power arsenal that could help address Colorado's pitching struggles. His slider also stands out as a legitimate weapon.

Rockies Select 6-foot-8 Reliever in Rule 5 Draft

The Colorado Rockies grabbed RJ Petit from the Detroit Tigers with the top selection in the Rule 5 Draft. The 26-year-old right-hander posted a 2.44 ERA across 66.1 innings between Double-A Erie and Triple-A Toledo in 2025, striking out 79 batters while walking just 22 and finishing with a 1.06 WHIP.

The Rockies newest Rule 5 Draft pick RJ Petit is an absolute mountain of a man.

6’8 300 lbs. pic.twitter.com/4jtkSljQGH

— Christian Saez🎙 (@DNVRSaez) December 10, 2025

Petit was passed over in the 2024 Rule 5 Draft, but his development over the past year made him one of the most attractive options available. His Triple-A numbers were particularly impressive, posting a 2.74 ERA with a 34.4% strikeout rate in 23 innings. The performance caught Colorado's attention as they searched for bullpen help.

Under Rule 5 Draft rules, Petit must remain on Colorado's active roster for the entire 2026 season or be offered back to Detroit for $50,000. The Rockies clearly view him as an immediate bullpen contributor rather than a developmental project.

How Petit's Arsenal Works at Triple-A

Here are more of my thoughts on RJ Petit https://t.co/jXxFnUu7TC pic.twitter.com/FvhbksIHeu

— Thomas Nestico (@TJStats) December 10, 2025

The foundation of Petit's success is a slider he leans on heavily, throwing it more than 40% of the time according to pitch tracking data. The breaking ball sits at 83.7 mph and generated a 41.7% whiff rate at Triple-A, with hitters missing on more than two out of every five swings. Analyst Thomas Nestico broke down the pitch on social media, noting it features a "tight two-plane break that Petit consistently locates low and away to generate whiffs and chases," per Nestico.

That slider works because of how it plays off his fastball. Petit's four-seamer sits at 95 mph, creating an 11-mph velocity gap that gives hitters timing problems. The heater itself produced a 33.3% whiff rate at Triple-A, and his height creates a steep downward angle that makes both pitches harder to square up. Hitters have to adjust to both the velocity difference and the plane change between offerings.

The biggest story in Petit's 2025 season was his changeup development. According to pitch data analyzed by Nestico, he threw the pitch at 87.7 mph and commanded it for strikes at an above-average rate, transforming himself from a two-pitch reliever into someone with a more complete arsenal. That improvement is why he got selected after being passed over in 2024. The change-up gives him a weapon against opposite-handed hitters and prevents batters from sitting on his fastball-slider combination.

The results speak to how well these pitches complement each other. Petit recorded a 30.1% whiff rate and 64.6% strike rate across his 2025 season, showing he can both miss bats and attack the zone. His 2.94 FIP suggested the performance was sustainable rather than luck-driven.

Addressing Colorado's Desperate Need for Arms

Colorado finished 2025 with a 6.65 rotation ERA that was worst in baseball by nearly 1.5 runs, and even their bullpen struggled at 5.18 ERA. Petit's ability to generate swings and misses while throwing strikes addresses exactly what plagued the entire staff.

The physical profile matters even more at Coors Field, where fly balls turn into extra-base hits at altitude. Petit's frame creates a downward plane that makes his pitches harder to elevate, and his slider works low in the zone to generate ground balls. For a team that won just 43 games, adding an arm with legitimate strikeout stuff represents a small but necessary step forward.

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