Greg Duncan begins his second year with the ThunderBolts and fourth as a pro in 2025. He originally signed on February 10, 2024. He had a 1.50 ERA and five saves in 13 games for the 2024 Bolts before splitting his second half of the season amongst the Mexican League, American Association and Atlantic League. Before joining the ThunderBolts, Greg pitched for three other Partner League teams, including the Gateway Grizzlies in 2021. He appeared in nine games for them (two starts) and had a 5.46 ERA. He also pitched in five combined games between stints with the Gary SouthShore RailCats and Winnipeg Goldeyes - both of the American Association - between 2021 and 2023.

Duncan pitched one season at Radford University, going 6-3 with a 4.38 ERA over 13 starts. Prior to that, he was a four-year player at the University of Virginia-Wise. With the Cavaliers, he compiled an 18-11 record and 3.58 ERA. He was a Second Team All-Mountain East selection in 2019 and Honorable Mention All-Mountain East as a sophomore in 2018. He departed UVA-Wise as the school's all-time leader in innings pitched (221) and ranked third in school history in strikeouts (200) and fourth in ERA. He attended Westfield High School in Chantilly, Virginia.