Royals LHP Justin Lamkin turns Arizona Fall League into a curveball classroom after shoulder setback

A year after the Royals first pushed Justin Lamkin to add a new breaking-ball look, the 22-year-old is back in Glendale to reestablish his health and finish the development of a “baby spike” curve.

By The Apex Times Newsroom2 min readAI-assisted Apex article

Justin Lamkin did not throw a curveball in college, so the Kansas City Royals assigned him that task when they began his first major development stretch at spring training last year. One season later, the left-handed pitching prospect is using the Arizona Fall League to continue that work, with the goal of giving right-handed hitters another weapon beyond a slider.

The context for the refresher matters: Lamkin’s regular-season time ended early after a left-shoulder injury cut him off before he could keep building. The Royals have said the issue was not structural, and he returned to the desert to reestablish health and pick up where he left off with the curve development.

Through his first two AFL starts, the curve has shown up more regularly, and the results have backed it up. In his Oct. 6 debut after 4 1/2 months away, he threw 13 curveballs out of 53 pitches (25 percent), allowing five runs (four earned) over three innings, with both strikeouts coming on the curve.

Then, in his second start on Thursday, Lamkin increased his curve usage and improved the outing. He threw 23 curves on 62 pitches (37 percent) and allowed one earned run on one hit while striking out three over four innings in a 17-8 road win at Glendale.

Part of the pitch’s evolution is tied to grip adjustments designed to create more vertical movement. The curve Lamkin is working on hooks his middle finger onto the baseball’s horseshoe and uses his pointer finger to add what he described as a “baby spike,” with the offering dropping about 1 foot more and sitting about 2-3 mph slower than his previous slider.

The Royals’ broader development track started before the injury. After beginning 2026 at High-A Quad Cities, Lamkin moved to Double-A Northwest Arkansas in mid-May and, over three Texas League starts before the shoulder setback, posted a 2.04 ERA with 53 strikeouts and 14 walks in 39 2/3 innings combined between the two stops.

The immediate competition for Lamkin’s curve in the AFL has been specific and encouraging. Through his two starts, batters produced 17 swings against a 78-81 mph curveball, with a whiff rate of 41.2 percent, including a strikeout on the pitch in the improved four-inning effort.

Why It Matters

For the Royals, Lamkin’s curve development is about creating a fuller breaking-ball plan, especially against right-handed hitters who have to track a slider already.
Returning to the AFL after a shoulder issue turns October innings into an evaluation of health and command timing, not just pitch design.
If Lamkin can pair a usable curve with his mid-90s fastball, it supports the organization’s long-term thesis that he can become more than a two-pitch lefty.
More broadly, Arizona Fall League reps give Kansas City an extended look at whether the curve that began as a development assignment can translate into consistent in-game performance.

Sources

Key Facts

The Royals assigned Justin Lamkin to add a curveball during his first major development assignment at spring training last year.
Lamkin’s 2026 regular season ended early after a left-shoulder injury before May 25.
In his AFL debut on Oct. 6, Lamkin threw curves 25 percent of the time (13 of 53 pitches) and allowed five runs (four earned) in three innings.
In a second AFL start on Thursday, he increased curve usage to 37 percent (23 of 62) and allowed one earned run with three strikeouts over four innings in a 17-8 win.
Lamkin’s curve grip includes a middle-finger horseshoe hook and a “baby spike” pointer-finger action, designed to add vertical movement.
Across his first two AFL starts, batters went 0-for-7 with the curve for seven whiffs, producing a 41.2 percent whiff rate on the pitch.