He first became interested in basketball at only six, when Halstead won the first of two consecutive Kansas state high school basketball championships. According to interviews, he and his brothers stuffed rags into a gunnysack which his mother sewed up to use as a basketball on the family farm. Later, after growing to a sturdy 6-foot-2, Rupp was a star on his Halstead High School team, averaging over 19 points a game in both his junior and senior years.