As a young man, Naismith (who had no middle name but adopted the initial “A.”) studied theology and excelled in various sports. In the autumn of 1891 he was appointed an instructor by Luther Halsey Gulick, Jr., head of the Physical Education Department at Springfield. Gulick asked Naismith and other instructors to devise indoor games that could replace the boring or dangerous exercises used at the school during the winter. For his new game Naismith selected features of soccer, American football, field hockey, and other outdoor sports but (in theory) eliminated body contact between players. Because his physical education class at that time was composed of 18 men, basketball originally was played by 9 on each side (eventually reduced to 5).

The first games employed half-bushel peach baskets as targets, so a stepladder was needed to retrieve the ball after infrequent goals. Naismith's original rules, prohibiting walking or running with the ball and limiting physical contact, are still the basis of a game that spread throughout the world.

In 1898 Naismith received an M.D. from Gross Medical College, Denver, Colo., afterward the University of Colorado School of Medicine. From that year until 1937 he was chairman of the physical education department at the University of Kansas, Lawrence, where he also coached basketball until 1908. In addition to basketball, he is credited with inventing the protective helmet for football players. The Naismith Memorial Basketball Hall of Fame, Springfield, Mass., was incorporated in 1959.