Nick Clausen began his boxing career with the Sparta Club in 1918. He became Danish champion in 1922, and in 1922 competed in the United States, winning the Metropolitan Championship. He was then declared a professional by the US Amateur Boxing Association, because he had sold his cups and trophies. Clausen fought as a professional from 1923-1941 in Sweden, Denmark, and the United States, with little success, and with very few fights. He finished with a career record of 3 wins, 6 losses, and 6 draws. He coached Finland’s 1928 Olympic boxing team and in the 1960s coached young boxers at his old Sparta Club.