According to one source, the Detroit Tigers earned their nickname from their orange striped socks. However, when they entered the American League in 1901, the Tigers wore blue and red striped socks. It’s possible a prior non-major league team in Detroit wore orange striped socks, but research does not support that theory.
A more likely reason for the Detroit Tigers nickname is in reference to the Detroit Light Guard, a famous military unit from Michigan that had performed bravely in the U.S. Civial War and the Spanish-American War. The unit was known as the “Fightin’ Tigers” because the crest they adopted featured a Tiger head.