KC Royals: Breaking down an inning of John McMillon

Pitcher John McMillon might be the KC Royals' biggest pitching development success story this season. He not only rose from Low-A Columbia to The Show within a season but completely turned around his prospect profile in the process. The scary thing is he is not all hype; he is producing.

There are a ton of reasons to like KC Royals pitcher John McMillon.

If you do not know who McMillon is, that is likely because you stopped watching the Royals this month. It is hard to blame fans for tuning out, as the team just had a 2-7 road trip. Trotting out pitcher Jordan Lyles and infielder Matt Duffy is not going to inspire interest from fans. But, those still watching will hopefully appreciate McMillon's story.

The Royals signed 25-year-old McMillon in 2020 as an undrafted free agent. McMillon was an MLB prospect, but the abbreviated draft that year made him available to the Royals. The Texas Tech alum looked every bit of an undrafted prospect to start his career.

He totaled 34 2/3 innings in Low-A across the 2021 and 2022 seasons. He struggled mightily in that span, with a 10.90 BB/9 and 6.23 ERA. But, his 13.75 K/9 remained elite and that proved some hope. The fastball and slider combination was lethal to opposing batters, but poor control negated that combination's effects. 2023 was a key year for McMillon, already much older than the average Low-A player. Thankfully, he turned things around in big fashion.

McMillon started the season in Columbia with nine dominating performances. That continued to High-A Quad Cities, where his walk and strikeout rates surprisingly got better. Then, a promotion to Double-A did not slow down McMillon at all. Count that up. Within two and a half months, McMillon was promoted twice with little learning curve at each level. He pitched 51 1/3 innings across all those levels, with a 2.45 ERA, .955 WHIP, 16.0 K/9 and 4.4 BB/9. The walks are high, sure, but all that together makes for an elite minor-league reliever.

The Royals did not waste any time getting McMillon to the majors. They activated him straight from Northwest Arkansas and made his debut against the Seattle Mariners on Aug. 17, 2023. Injuries and poor play are calling cards of the Royals bullpen this season, so the team cycling through relievers quickly is not surprising. But, McMillon rising this quickly was surprising.

As I said, McMillon is not just an arm that could succeed in the bullpen, He is doing it right now. He has four single-inning appearances, allowing only one hit, a home run, with eight strikeouts to no walks. A 2.52 FIP speaks to his stuff playing at the major-league level, albeit with an unsustainable 18.0 K/9. So, with McMillon looking so strong, I want to walk through his Sunday appearance against the red-hot Mariners in Seattle.