Moselle grew up in Wisconsin and attended University of Wisconsin-Superior (UWS) starting in 1946 after serving two years in the U.S. Army during World War II. Playing as a halfback for the school's football team, he set a number of records, including most rushing yards in a career and most touchdowns in a game, season and career. He was the team's captain and was chosen as an all-conference player. The NFL's Cleveland Browns selected him in the later rounds of the 1950 draft after he was recommended to Cleveland head coach Paul Brown by the coach of one of his opponents in college. The Browns won the NFL championship in 1950, but Moselle was traded the following year to the Green Bay Packers. He played two seasons in Green Bay and one season for the Philadelphia Eagles before playing a final season in the Canadian Football League for the Calgary Stampeders in 1955.