Dietz pitched just two years for the Crusaders, but made an immediate impact on the program. He was the top starting pitcher on the 1957 team, posting an 8-1 record on a team which finished the season 16-3 and ranked second in New England. In 1958, Dietz accounted for six of the team's 13 regular season victories. The Crusaders won the East Regional that year, and Dietz won two games as Holy Cross qualified for the College World Series. Dietz beat eventual-champion USC 3-0 in the opener, the only time USC would be shut out all season. The Crusaders finished third in the tournament, surpassed only by the 1952 Holy Cross team which won the CWS. Dietz was selected to the “All World Series Team” and was also chosen first team All New England. He was 17-3 (85% winning percentage) as a Crusader, and posted a career ERA of just 1.98. At the conclusion of the 1958 season, he signed a professional contract with the St. Louis Cardinals organization.