One of the Pittsburgh Pirates’ most interesting relief prospects in their system right now is right-hander Derek Diamond. The 2022 sixth-round pick transitioned to the bullpen in 2025, but struggled with injuries. He stayed healthy for most of 2026 and could make an impact at the MLB level in the near future.
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Diamond pitched 58 innings over four levels of the minor leagues. He spent most of his season at Triple-A Indianapolis. Overall, he posted a 2.48 ERA, 3.14 FIP, and a 1.02 WHIP. He struck out just under a quarter of the batters he faced (24.6% K%), while walking 3.9% of batters. Diamond also allowed just four home runs with a respectable 45.3% ground ball rate.
Diamond’s peripherals were also good. His 20.7% K-BB% was the second-best among Pirates’ minor league hurlers who threw at least 50 innings this year. At Triple-A, he induced a 28.2% whiff rate, which was above the league average rate of 26.2%. Diamond held opposing batters to just a .289 xwOBA against him.
Diamond’s primary pitch is a mid-90s four-seam fastball. He throws his four-seamer with above-average spin, around 2350 RPM, with 15 inches of induced vertical break. His fastball isn’t flat either, with 7.6 inches of arm-side break. Diamond’s go-to breaking pitch is a mid-80s slider with nearly nine inches of glove-side break on average. His secondary breaking pitch is an upper-70s curveball with nearly 50 inches of drop and 15 inches of glove-side movement. He rounds out his pitch arsenal with a mid-80s change-up and a low-90s sinker; however, he used both pitches less than 10% of the time this year.
Diamond’s release point also adds a level of deception to his stuff. At 6.9 feet, he adds one whole tick to his perceived velocity. That means his fastball, which clocks in around 95 MPH on the radar gun, reaches the plate more like a 96 MPH fastball. For reference, Cristopher Sanchez and fellow Pirates breakout reliever Yohan Ramirez both averaged 6.9 feet of extension, putting both above the 85th percentile.
The Pirates haven’t had much luck with relievers they added to the 40-man roster in recent years. Colin Selby didn’t impress after the Pirates protected him from the Rule 5 draft after the 2022 campaign. Brandan Bidois posted a sub-1.00 ERA in 2025 in the minor leagues, but struggled in 2026 before the Pirates traded him to the Miami Marlins. However, Diamond is different. Both Bidois and Selby had a walk rate over 9%. Both struggled to get ahead in the count compared to Diamond. Selby had just a 45% first-pitch strike rate in 2022, and Bidois sat at 50.9% in 2025. Meanwhile, Diamond sat at 56.5%. Although he had a lower K% than both Bidois in 2025 and Selby in 2022, all three had a similar called and swinging strike rate (CSW%). Diamond sat at 28.7%, while Bidois came in at 28.9% in 2025, and Selby sat at 29.4% in 2022.
Regardless of how the Rule 5 draft plays out because of the potential lockout, Diamond has done everything in his power to earn a 40-man roster spot. If the Pirates give him a spot in their bullpen early into next season, he’d likely begin his career in a lower-leverage role; however, given his stuff and solid control, he could work himself into higher-leverage innings before the end of next season.
