Maybe he wanted to be drafted by an NBA team, the legendary Boston Celtic John Havlicek not only was drafted by an NFL team, the Cleveland Browns, before Boston drafted him. He went to the Browns training camp in 1962 and played in at least one preseason game. The record shows that he made a key block that sprung Jim Brown for a 45 yard TD run.
When coach and former owner Paul Brown could see that Havlicek wouldn't make the team that year, he released 'Hondo' so that he could start his basketball career. He signed with the Celtics shortly afterward.
In 1966, the Browns offered him $40,000 to play. Supposedly a couple other teams made offers. Red Auerbach and the NBA commissioner complained to Pete Rozelle about tampering, and that was that.