From Bulbapedia, the community-driven Pokémon encyclopedia.
Street vendors set up for the festival
The Nomads Independence Day is a week-long festival celebrated in Fuchsia City annually. It commemorates the independence day of various nomadic tribespeople in Kanto. It appears exclusively in the manga series The Electric Tale of Pikachu.
Every year, members of several nomadic tribes congregate in the Fuchsia City area for a series of over 100 Pokémon races. The races are chiefly held amongst Pokémon of the same species, such as the Fuchsia Rattata Race and the Parasect Race. The festival culminates at the end of the week with the Fuchsia Free-For-All Race, the biggest and most well-known of all the Independence Day races. The Free-For-All Race alone generates many tourists in Fuchsia City.
Aside from the races, there are other attractions during the Nomads Independence Day celebrations as well, such as street vendors.