Mark Stewart Appel (born July 15, 1991) is an American professional baseball pitcher who is a free agent.

Appel did not sign after being selected eighth overall by the Pittsburgh Pirates, returning to Stanford for his senior season.

He returned to the Phillies organization in March 2021 to attempt a comeback, and made his major league debut in June 2022.

Appel attended Monte Vista High School in Danville, California,[1] where he played for the baseball and basketball teams.

Appel began his collegiate career as a reliever, making 24 relief appearances, but also starting three games.

[7] In the summer of 2010, he played for the Newport Gulls of the New England Collegiate Baseball League (NECBL), posting a 6–1 win–loss record and 1.87 ERA in n 43+1⁄3 innings.

[10] Appel was projected as a potential first overall pick in the 2012 Major League Baseball draft,[1] but reportedly rejected an offer from the Astros for a $6 million signing bonus.

Due to the high perceived bonus demands, Appel fell in the draft to the eighth overall selection, where he was chosen by the Pittsburgh Pirates.

[12] Appel graduated from Stanford after the fall semester, receiving a bachelor's degree in management science and engineering.

[15] After making two starts for Tri-City, the Astros promoted Appel to the Quad Cities River Bandits of the Single-A Midwest League.

[19] For Tri-City and Quad Cities, Appel pitched to a 3–1 record in 10 games started, with a 3.79 ERA and 33 strikeouts with nine walks in 38 innings.

[22] He started for the Astros in their final spring training game, throwing three scoreless innings against the Rojos del Águila de Veracruz of the Mexican League.

[23] The Astros assigned Appel to the Lancaster JetHawks of the High-A California League at the start of the regular season.

[26] After pitching to a 2–5 record and a 9.74 ERA in 12 starts for Lancaster, the Astros promoted Appel to the Corpus Christi Hooks of the Double-A Texas League.

The Astros then assigned him to the Salt River Rafters of the Arizona Fall League after the season, where he had a 2.61 ERA and 24 strikeouts to eight walks in 31 innings pitched, while limiting opponents to a .167 batting average against.

[33] On December 12, 2015, the Astros traded Appel, Vince Velasquez, Brett Oberholtzer, Tom Eshelman, and Harold Arauz to the Philadelphia Phillies in exchange for Ken Giles and Jonathan Araúz.

[47] Appel made his major league debut on June 29, pitching one inning of relief against the Atlanta Braves.