According to the BBC, athletes are believed to run counterclockwise on the track due to the early use of horse tracks for running events. Horses raced around the oval in the same direction. Although not universal, until the 1950s, the practice was commonplace in many countries by the early 1900s.
The first four modern Olympic Games had athletes run in a clockwise direction. After this, Olympic organizers switched to counterclockwise running due to its popularity in America. Both Oxford and Cambridge Universities continued to have athletes run in a clockwise direction until the middle of the century. A shift in thinking occurred in 1954, when Roger Bannister became the first man to run the mile in under four minutes. In achieving the feat, Bannister ran in a counterclockwise direction.