In 1989, Diaz was hired as the head football coach for Bemidji State as the successor to John Peterson.[8] Diaz inherited a team that came off of a 1–9 season and brought them to a 4–5 record in his first season.[9] He was named NIC Coach of the Year following the season.[9][10] Over the next five seasons his team would not win more than two games. His best season during that five-year stretch was in 1991 when he led the team to a 2–7 record. In his last season in 1995, he led the team to a 3–7 record and was named NSIC Coach of the Year.[11] Diaz resigned following the season,[12] stating "personal reasons" as the reason.[11] He ended his seven-year career with Bemidji State with an overall record of 13–55,[13] with his best season coming in his first when they finished 4–5.
During Diaz's tenure with Friends he served as an assistant basketball coach and head track and field coach.[6][7] When he was hired as the offensive line coach by Moorhead State in 1983, he also served as an assistant track and field coach.[6]
From 1983 to 1988, Diaz was an assistant athletic director for Moorhead State. In 2006, he was hired as an assistant athletic director for his alma mater, Baldwin–Wallace.[1] He was promoted to full-time athletic director in 2008.[1] He maintained the position until June 30, 2020, after he announced his retirement on June 15.[14][15]