William Johnston Clymer (December 18, 1873 – December 26, 1936) nicknamed "Derby Day Bill", was an American professional baseball player and manager.

After his playing career, Clymer became a successful minor league manager.

At the age of 17, Clymer appeared in three games for the Philadelphia Athletics of the American Association.

[1] Clymer died at the age of 63 in his hometown of Philadelphia, and is interred at North Cedar Hill Cemetery.

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