As a freshman at Florida State in 2023, Arnold appeared in 24 games and went 2–5 with a 6.34 ERA over 44 innings.[3] He played in theCape Cod Baseball League for theHyannis Harbor Hawks after the season and was named an All-Star.[4][5] As a sophomore in 2024, Arnold started 18 games and posted an 11–3 record, a 2.98 ERA, and 159 strikeouts over105+2⁄3 innings and was named an All-American.[6] After the season, he was selected to play for theUSA Baseball Collegiate National Team and was the starting pitcher in a combined no-hitter in a games versus Chinese Taipei.[7]
Entering the 2025 season, CBS ranked Arnold is considered to be one of, if not, the best prospect going into the 2025 MLB Draft.[8] He returned to Florida State as the team's number one starter.[9]
