Lately there were new personal documents found in his family's basement. It says that his students got bored during the winter months when they couldn't play outdoor soccer and football. Naismith needed to invent a strenuous game that could be played on small indoor courts.
He tried to adapt lacrosse and football to be played inside. He even introduced his students to a slew of invented games like Hylo Ball, Scruggy Ball and Association Football. None of them took.
You can read more about it here:
http://sports.espn.go.com/nba/news/story?id=2660882