John Joseph "Sadie" McMahon (September 19, 1867 – February 20, 1954) was an American professional baseball player who played pitcher in the Major Leagues from 1889 to 1897. McMahon played for the Philadelphia Athletics, Baltimore Orioles, and the Brooklyn Bridegrooms.

Sadie McMahon
Pitcher
Born: (1867-09-19)September 19, 1867 Wilmington, Delaware, U.S.
Died: February 20, 1954(1954-02-20) (aged 86) New Castle, Delaware, U.S.
Batted: Right Threw: Right
MLB debut
July 5, 1889, for the Philadelphia Athletics
Last MLB appearance
July 12, 1897, for the Brooklyn Bridegrooms
MLB statistics
Win–loss record	173–127
Earned run average	3.51
Strikeouts	967
Teams
Philadelphia Athletics (1889–1890) Baltimore Orioles (1890–1896) Brooklyn Bridegrooms (1897)

McMahon was born in Wilmington, Delaware and grew up in the Henry Clay Village area. In 1954, McMahon died and was buried in St. Joseph on the Brandywine Church Cemetery in Wilmington. He was inducted into the Delaware Sports Museum and Hall of Fame in 1979.