Harding was selected by his hometown Detroit Pistons in the 1962 NBA draft as the 29th overall pick and became the first NBA player to be drafted without playing in college. The legality of the selection was challenged immediately as the NBA rules stated a player could be drafted if they did not plan to enter college but needed to have been out of school for a full year. Harding's prep school stint in Tennessee brought this into question and he was ultimately unable to sign with the team due to the technicality in his eligibility. Pistons Director of Staff Fran Smith knew of the issue but stated that the team utilised the advantage of draft protection as several other teams had shown an interest in signing Harding. In July 1962, National Basketball Association Board of Governors ruled that the Pistons could retain his player rights but he could not be signed until the 1963–64 NBA season. Harding instead began his professional career in the Midwest Professional Basketball League (MPBL) with the Toledo Tartans and Cook's/Holland Oilers during the 1962–63 season. He was selected by the Detroit Pistons again in the 1963 NBA draft as the 48th overall pick. Harding was signed by the Pistons, but was kept off the roster for disciplinary reasons as he was involved in a police investigation. In 1963, Harding was assigned by the Pistons to a five-day clinic with Dr. W. M. Hardy, a chiropractor in Waynesville, North Carolina, who served as an advisor to the Pistons, and was taught how to shoot a basketball. Harding began the clinic with only the use of a right-handed hook shot but left with the ability to "shoot every shot in the book".
