Frederick William "Fritz" Clausen (April 26, 1869 – February 11, 1960) was a professional baseball pitcher in Major League Baseball who played between 1892 and 1896 for the Louisville Colonels, and Chicago Colts.

Clausen batted right-handed and threw left-handed.

In a four-season career, Clausen posted a 16–22 record with 134 strikeouts and a 3.58 ERA in 324⅓ innings pitched, including 36 complete games and two shutouts.

Clausen died from injuries suffered in an accidental fall in Memphis, Tennessee, at the age of 90.

This biographical article relating to an American baseball pitcher born in the 1860s is a stub.