The Milwaukee Brewers selected Small in the first round, with the 28th overall selection, of the 2019 Major League Baseball draft. He signed for $1.8million. He made his professional debut with the Arizona League Brewers, and, after two games, was promoted to the Wisconsin Timber Rattlers. Over seven starts between the two teams, he went 0–2 with a 0.86 ERA, striking out 36 over 21 innings. He did not play a minor league game in 2020 due to the cancellation of the season.
Small began the 2021 season with the Biloxi Shuckers and was promoted to the Nashville Sounds during the season. That June, he was selected to play in the All-Star Futures Game. Over 18 starts in 2021, Small went 4–2 with a 1.98 ERA and 92 strikeouts over 77+1⁄3 innings.
Small was assigned to Triple-A Nashville to begin the 2022 season. On May 30, 2022, Small was selected to the 40-man roster and promoted to the major leagues for the first time to make a spot start against the Chicago Cubs.
Small was optioned to Triple-A Nashville to begin the 2023 season. He made two major league appearances for Milwaukee on the year, struggling to an 11.25 ERA with 6 strikeouts across 4.0 innings of work. On February 1, 2024, Small was designated for assignment by the Brewers.
San Francisco Giants
On February 5, 2024, the Brewers traded Small to the San Francisco Giants in exchange for cash considerations. He was placed on the 60–day injured list to begin the season after suffering a moderate right oblique strain. Small was activated from the injured list on August 16 and was subsequently optioned to the Triple–A Sacramento River Cats. On November 22, the Giants non–tendered Small, making him a free agent.
On December 5, 2024, Small re–signed with the Giants organization on a minor league contract. He made seven appearances for Sacramento in 2025, struggling to a 7.11 ERA with six strikeouts across 6+1⁄3 innings pitched. Small elected free agency following the season on November 6, 2025.
Pitching style
Small features a lively low- to mid-90mph fastball—scouts often described it as a "rising" fastball—a curveball and changeup. He has been known to vary his windup timing on his pitches, to give him an advantage over hitters, similar to pitchers such as Marcus Stroman and Johnny Cueto.