Bailey Falter (born April 24, 1997) is an American professional baseball pitcher for the Kansas City Royals of Major League Baseball (MLB). He has previously played in MLB for the Philadelphia Phillies and Pittsburgh Pirates.

Born in Chino Hills, California, Falter grew up idolizing pitcher Sandy Koufax. He attended Chino Hills High School, pitching a no-hitter for their baseball team in 2013. The Phillies selected Falter in the fifth round of the 2015 MLB draft, and he signed with the team that year. His rise through the Phillies' farm system was disrupted by an elbow injury in 2019 and the subsequent cancellation of the 2020 minor league season. Falter made his MLB debut with the Phillies in 2021, and he spent the next three seasons alternating between Philadelphia and the Triple-A Lehigh Valley IronPigs, serving as both a starting pitcher and a reliever. The Pirates acquired Falter in 2023, adding him to their starting rotation.

Falter was born April 24, 1997, in Chino Hills, California. He became interested in baseball when his father Darwin encouraged him to do a school project on Sandy Koufax, a pitcher whom Falter then sought to emulate. In 2011, Falter helped take the United States national under-14 baseball team to a gold medal at the COPABE Junior Olympic Pan Am Championship in Venezuela, pitching a scoreless inning in relief of the championship game. As a student at Chino Hills High School, Falter was classmates with future National Basketball Association (NBA) player Lonzo Ball and developed a friendship with the Ball family. As a sophomore with the Chino Hills Huskies in 2013, Falter pitched a no-hitter, striking out 16 batters in an 11–0 victory over Bloomington High School. In his final season with Chino Hills, Falter had a 6–2 win–loss record, a 1.20 earned run average (ERA), and he struck out 97 hitters in 75+2⁄3 innings pitched. He pitched four complete games and two shutouts while securing two saves.

The Philadelphia Phillies of Major League Baseball (MLB) selected Falter in the fifth round, with the 144th overall pick, of the 2015 MLB draft. At the time, Falter had committed to playing college baseball for the UC Santa Barbara Gauchos. He came to terms with the organization on a $420,000 signing bonus and was assigned to the Rookie-level GCL Phillies. Although his pitch velocity was not overpowering, Falter displayed good command in the Gulf Coast League, and he was 1–2 with a 3.45 ERA in his first season of professional baseball, striking out 25 batters in 28+2⁄3 innings. The next year, the Phillies promoted Falter to the Low-A Williamsport Crosscutters, where he was part of a group of young Phillies prospects that also included Adonis Medina, JoJo Romero, and Cole Irvin. Falter struggled in his first two Williamsport outings, and his performance improved as he demonstrated increased confidence on the mound. He also made a mechanical adjustment partway through the season, using his lower body to generate more velocity on his pitches. In 13 New York–Penn League games, Falter was 1–6 with a 3.17 ERA, recording 59 strikeouts in 59+2⁄3 innings.

Falter joined the Single-A Lakewood BlueClaws for the 2017 season, where the then-19-year-old pitcher was one of the youngest players on the roster. In 21 South Atlantic League starts that season, Falter went 8–7 with a 2.99 ERA, striking out 105 batters in 114+1⁄3 innings and impressing director of player development Joe Jordan. He continued his rise through the Phillies' farm system with a promotion to the High-A Clearwater Threshers in 2018. After going 4–2 with a 3.08 ERA in the first half of the season, Falter was named a Florida State League midseason All-Star that June. He missed about a month of the season, spending July 8 to August 7 on the disabled list. In 17 starts for Clearwater, Falter finished the year 8–4 with a 3.36 ERA, recording 83 strikeouts in 93+2⁄3 innings. After the regular Minor League Baseball season, he joined the Indios de Mayagüez of the Liga de Béisbol Profesional Roberto Clemente. Falter went 2–0 with a 0.42 ERA in five starts there, striking out nine across 21+1⁄3 innings.

In 2019, Falter was named to the six-man starting rotation for the Double-A Reading Fightin Phils. His season ended on July 6, when he sustained an ulnar collateral ligament injury of the elbow. The injury was not severe enough to necessitate Tommy John surgery, and Falter was shut down from throwing to rest his arm. Before his injury, Falter made 14 starts for Reading, during which he went 6–5 with a 3.84 ERA and struck out 62 batters in 77+1⁄3 innings. When the 2020 Minor League Baseball season was cancelled due to the effects of the COVID-19 pandemic, Falter was not assigned to the Phillies' alternate training site. Instead, he returned home to California and spent the season putting on muscle mass. At the end of the 2020 season, the Phillies added Falter to their 40-man roster, protecting him from being claimed by another team in the Rule 5 draft.

The Phillies invited Falter to spring training in 2021, at the end of which he was assigned to the team's 30-player taxi squad. Falter made his MLB debut on April 25, pitching two innings in relief during Philadelphia's 12–2 loss to the Colorado Rockies. After pitching a scoreless seventh inning, he allowed a two-run home run to C. J. Cron in the eighth. After that outing, Falter was sent to the Triple-A Lehigh Valley IronPigs, where he established himself as a consistent presence in the starting rotation. He was recalled back to Philadelphia on June 15, where he served as the team's long reliever behind starters Spencer Howard and Vince Velasquez. He missed most of July with two separate stints on the COVID-19 injured list: once as a close contact of Alec Bohm, and again when he tested positive for the COVID-19 virus. Falter returned to the team on August 15, relieving Aaron Nola in a 7–4 loss to the Cincinnati Reds. He finished his rookie season with a 2–1 record and 5.61 ERA in 22 major league games, recording 34 strikeouts across 33+2⁄3 innings. In eight appearances for Lehigh Valley, he was 2–0 with a 1.76 ERA and 44 strikeouts across 30+2⁄3 innings.

Despite making the Phillies' 2022 Opening Day roster out of spring training as a reliever, Falter was sent down to Lehigh Valley at the end of April so that he could be stretched out into a starting pitcher. Falter never found a consistent role in Philadelphia or Lehigh Valley during the 2022 season: between April 26 and September 17, he was called up to the majors seven different times, filling in for injured starters Zach Eflin and Zack Wheeler, before being sent back to the IronPigs. He ultimately made 20 major league appearances that season, including 16 starts. In that time, he went 6–4 with a 3.86 ERA and struck out 74 batters in 84 innings. Falter also started nine games for the IronPigs, going 4–1 with a 1.91 ERA and 49 strikeouts in 47 Triple-A innings. The Phillies reached the MLB playoffs for the first time since 2011, and Falter made his postseason debut when he started Game 4 of the 2022 National League Championship Series against the San Diego Padres. His outing lasted only 24 pitches, as he allowed four runs before being relieved in the first inning, but the Phillies came back to win the game and ultimately take the series. Falter did not appear in the 2022 World Series, which the Phillies lost to the Houston Astros in six games.