William Riley Ritchie Sr. (January 25, 1876 – January 18, 1970) was an American college football player and coach, mathematics professor, and civil engineer. He was the second head football coach at Baylor University, serving for on year, in 1901 and compiling a record of 5–3. He was also the chairman of Baylor's mathematics department. Ritchie graduated in 1900 from the University of Georgia, where he played football.