Prior to playing collegiately at West Point, Christiansen enjoyed a very productive and accolade-filled career while at Nansemond-Suffolk Academy. As both a junior and senior, Christiansen was named the Virginia Independent Schools Athletic Association’s State Defensive Player of the Year. He was a three-time all-state and all-conference selection and won the VISAA State Championship as a senior in 2015. By the time he graduating, he was the VISAA all-time leader in career tackles with 436.
Christiansen did not redshirt in his first year, instead playing on special teams and sparingly on defense. He recorded just two tackles that year.