Freestyle skiing is an acrobatic form of technical and aerial skiing. It is organized into a number of different disciplines, although there are no impartial authorities for managing the sport internationally. Freestyle skiing first began to be taken seriously in the 1960s and early 1970s, when it was often known as "hot-dogging." Bob Burns pioneered this style in Sun Valley, Idaho beginning in 1965. In the late 1960s other followers of the style included Wayne Wong, Roger Evans, John Clendenin, Bob Salerno, and Tom LeRoy. Some people thought that this style of skiing was too dangerous and did not want it to be an Olympic sport. The free-form sport had few rules and wasn't without danger; knee injuries became a common phenomenon for professional freestylers. The International Ski Federation (FIS) recognized freestyle as a sport in 1979 and brought in new regulations regarding certification of athletes and jump techniques in an effort to curb the dangerous elements of the competitions. The first World Cup series was staged in 1980 and the first World Championships took place in 1986 in Tignes, France.