William H. Geer[1] (died September 30, 1928),[1] was an American Major League Baseball player who played most of his career as a shortstop for five seasons and a total of seven teams.

Geer made his professional baseball debut for the New York Mutuals of the National Association.

The following season, while playing for the New Haven Elm Citys, he was arrested along with his roommate, Henry Luff, for burglary of several hotel rooms.

[2] At age 15 years 63 days, he is credited as the youngest player to ever appear in a Major League Baseball game.

There is controversy about his age, or the fact that the National Association has not been officially credited as a "major league".