 His twin brother, Eddie, was also a major league infielder.O'Brien attended Saint Mary's High School in South Amboy, now Cardinal McCarrick High School, where he has been inducted into the school's sports hall of fame.O'Brien attended Seattle University, where he played on the basketball team for the Chieftains (along with his brother Eddie) and scored 43 points in a stunning 84–81 upset over the Harlem Globetrotters on January 21, 1952.