McMillon was initially drafted by the Rays in 2016, but he opted to play collegiately at Texas Tech University. In 2019, the Tigers drafted McMillon, but he returned to the Red Raiders for his senior year. McMillon went undrafted in the five-round 2020 MLB draft but was signed by the Royals. McMillon worked his way through the Royals system, displaying the ability to miss bats, but with a penchant for issuing free passes. After a stint with Double-A Northwest Arkansas where McMillon registered a .87 ERA with 30 strikeouts in 20.2 innings, McMillon was summoned to the Show in mid-August. McMillon managed to make four one-inning appearances before he was shut down for the season with a right forearm strain. McMillon impressed, allowing just one earned run while punching out eight in four innings. He's expected to be healthy in the spring and be a key component of the Royals bullpen, perhaps in a late-inning capacity. If McMillon can keep walks under control, he's dominant enough to be a fantasy asset, even if he's not collecting saves or holds. Read Past Outlooks