Mosley, from Newark, New Jersey, played college basketball at Seton Hall University in nearby South Orange.[2] He played for the Pirates from 1973–74 to 1976–77 where compiled career totals of 1,441 points and 1,263 rebounds.[2] Mosley's 15.2 rebounds per game for his career lists high on the NCAA's all-time list, and his 16.3 per game as a senior led all of NCAA Division I.[3]
The Philadelphia 76ers selected him in the first round (20th overall) in the 1977 NBA draft. After two years in the league with two different teams, Mosley embarked on his international professional career.