As a freshman at Miami in 2018, McMahon appeared in six games (four starts) in which he went 1–1 with a 4.44 ERA over 26+1⁄3 innings.[8] He missed time during the season after undergoing knee surgery.[9] In 2019, his sophomore year, he made only 12 starts on the season due to an arm injury - over 60+1⁄3 innings, he pitched to a 3–2 record and a 3.72 ERA with 67 strikeouts.[10][11] That summer, he played for the USA Baseball Collegiate National Team.[12][13][14] As a junior in 2020, McMahon went 3–0 with a 1.05 ERA over four starts before the college baseball season was cut short due to the COVID-19 pandemic.[15]
Professional career
McMahon was selected by the Colorado Rockies in the second round (46th overall) of the 2020 Major League Baseball draft.[16] He signed for $1.6 million.[17] He did not play a minor league game in 2020 due to the cancellation of the minor league season caused by the pandemic.[18]
McMahon was assigned to the Spokane Indians of the High-A West for the 2021 season, appearing in 22 games (making twenty starts) and going 10-3 with a 4.17 ERA and 119 strikeouts over 114+1⁄3 innings.[19] He opened the 2022 season on the injured list with a lat strain.[20] He pitched a total of 28+2⁄3 innings for the year between the Rookie-levelArizona Complex League Diamondbacks and Spokane, going 1-0 with a 5.34 ERA and 25 strikeouts.[21] For the 2023 season, McMahon was assigned to the Hartford Yard Goats of the Double-AEastern League.[22] Over 15 starts, he went 2-3 with a 5.91 ERA and 66 strikeouts over 67 innings. He was selected to play in the Arizona Fall League for the Salt River Rafters after the season.[23]
