Robert Louis "Bob" Arnzen (born November 3, 1947) is a retired American basketball and baseball player.
Born in Covington, Kentucky, Arnzen graduated from St. Xavier High School in Cincinnati, Ohio in 1965. He then played collegiately for the University of Notre Dame.
Arnzen was selected by the Detroit Pistons in the 8th round (93rd pick overall) of the 1969 NBA draft. He played for the New York Nets (1969–70) and Indiana Pacers (1972–74) in the ABA for 56 games (winning the 1972–73 ABA Championship) and for the Cincinnati Royals (1970–71) in the NBA for 55 games.
Arnzen additionally played Minor League Baseball for the Gulf Coast Expos (1969), West Palm Beach Expos (1969–71), Winnipeg Whips (1971), Québec Carnavals (1972), and Peninsula Whips (1972).