Maddox graduated from high school in 2009 as the top catcher in the state of Florida, having batted .544 in his senior year.

[2] Instead, he played college baseball at the University of Florida,[1] where he was teammates with future MLB catcher Mike Zunino.

[1] Initially a catcher and infielder, he made a total of 53 appearances as a pitcher in 2011 and 2012, striking out 78 and walking 14 in 82+1⁄3 innings, while compiling a 1.86 earned run average (ERA).

Maddox made his MLB debut on June 17, 2017, pitching the seventh inning in a Red Sox loss to the Houston Astros; he retired the side without allowing a baserunner.

[6] He finished the regular season with 13 appearances for the 2017 Red Sox, allowing just one earned run in 17+1⁄3 innings pitched (0.52 ERA), with 14 strikeouts and two walks.

[7] He made two one-inning appearances against the Houston Astros, allowing one earned run (4.50 ERA), with two strikeouts and two walks, as the Red Sox lost to the eventual World Series champions.

[12] On September 19, Maddox had surgery on his right rotator cuff with what was described as a right shoulder strain;[13] he did not play in any MLB games during 2018.