San Francisco 49ers In January 1959, Christiansen announced that he was retiring as a player to accept a position as an assistant coach with the
San Francisco 49ers under head coach
Red Hickey. He served as a defensive backfield coach with the 49ers for four years, from
1959 to
1962. In late September
1963, with the 49ers in the midst of a 10-game losing streak, including all five pre-season games and the first three regular-season games of the 1963 season, Hickey resigned, and Christiansen, at age 34, took over as the 49ers' head coach. In that season's final 11 games, the 49ers won only twice, but held the distinction of being the only team to defeat the eventual NFL champion
Chicago Bears. Over the succeeding four years, San Francisco continued to struggle, with Christiansen's best season coming in
1965 when the team was 7–6–1. The 49ers began the
1967 season with five wins in their first six games, but won only two more games the remainder of the campaign, resulting in Christiansen's dismissal on December 20, ending his tenure with a record of 26–38–3.
Colorado State In January 1968, Christiansen was hired by his alma mater,
Colorado State, as a consultant to review and make recommendations concerning the university's athletic program.
Stanford In April
1968, Christiansen was hired as an assistant coach under
John Ralston at Stanford. During this period, Stanford pulled off consecutive
Rose Bowl upsets of
Ohio State and
Michigan, both previously undefeated. In January
1972, Ralston left to coach the NFL's
Denver Broncos, and Christiansen was promoted to head coach. Christiansen spent five years as Stanford's head coach, compiling a winning record each year and a 30–22–3 overall record. He was criticized for starting Mike Cordova rather than
Guy Benjamin at quarterback during the
1975 season and for switching between quarterbacks during the
1976 season. One day prior to the final game of the 1976 season, Stanford announced that it was terminating Christiansen as its head coach.
Kansas City Chiefs In March
1977, Christiansen was hired as an assistant coach, responsible for running backs, under
Paul Wiggin with the
Kansas City Chiefs. Wiggin was fired in the middle of the season, as the Chiefs compiled a 2–12 record.
Seattle Seahawks In April
1978, Christiansen was hired by the
Seattle Seahawks, replacing Bob Holloway as the team's defensive backfield coach. He spent five years as the Seahawks' defensive backfield coach, from 1978 to
1982.
Atlanta Falcons In February
1983, Christiansen was hired by the
Atlanta Falcons as its secondary coach. In January 1984, Christiansen resigned his position with the Falcons after being diagnosed with cancer. ==Honors, family, and later years==