Will Klein (baseball)

William Boone Klein (born November 28, 1999) is an American professional baseball pitcher for the Kansas City Royals of Major League Baseball (MLB).

Amateur career
Klein attended Bloomington High School North in Bloomington, Indiana. As a senior in 2017, he pitched only $17 2⁄3$ innings after breaking his thumb, but still struck out thirty batters and compiled a 1.98 ERA. Unselected in the 2017 Major League Baseball draft, he enrolled at Eastern Illinois University where he posted a 6.62 ERA over $17 2⁄3$ innings as a freshman, a 5.11 ERA over $24 2⁄3$ innings as a sophomore, and a 3.33 ERA with 33 strikeouts as a junior in 2020 before the season was cancelled due to the COVID-19 pandemic.

Professional career
Klein was selected by the Kansas City Royals in the fifth round with the 135th overall pick of the 2020 Major League Baseball draft. He signed for $200,000.

Klein made his professional debut in 2021 with the Quad Cities River Bandits of the High-A Central. Over 36 relief appearances, he went 7–1 with a 3.20 ERA, 121 strikeouts, and 44 walks over $70 1⁄3$ innings pitched. MLB Pipeline named Klein the Royals' Pitching Prospect of the Year following the season's end. He missed the beginning of the 2022 season due to shin splints. He returned to play in mid-May with the Northwest Arkansas Naturals of the Double-A Texas League as a member of their starting rotation, but was later moved to the bullpen. Over thirty games (three starts), he went 1–1 with a 10.51 ERA, 55 strikeouts, and 51 walks over $43 2⁄3$ innings. He returned to the Naturals to open the 2023 season. In mid-June, he was promoted to the Omaha Storm Chasers of the Triple-A International League. He was selected to represent the Royals at the 2023 All-Star Futures Game. Over 49 appearances between Northwest Arkansas and Omaha, Klein went 1–5 with a 4.62 ERA, 93 strikeouts, and 39 walks over $64 1⁄3$ innings.

On November 14, 2023, the Royals added Klein to their 40-man roster to protect him from the Rule 5 draft. He was optioned to Triple–A Omaha to begin the 2024 season. On April 25, 2024, Klein was promoted to the major leagues for the first time following an injury to Alec Marsh.