He played fifteen seasons with the Washington Senators (1910–1918), Detroit Tigers (1919–1921), St. Louis Cardinals (1921–1923), Brooklyn Robins (1923), and New York Giants (1924).

[1] The Day Book in Chicago, Illinois described Ainsmith in their May 10, 1913 edition as "a gingery young receiver, throws well, can handle Walter Johnson and is a good batter.

Walter Johnson said that if Aimsmith was bleeding from being spiked by an opposing player, Ainsmith would refuse assistance from the team trainer, denying that he was injured.

[4] In 1913, as a member of the Washington Senators, Ainsmith was suspended by Ban Johnson for throwing dirt at umpire Peter McLaughlin.

[7][8] In 1925, Ainsmith promoted a tour of an American teenage female baseball team which he led through East Asia.