According to Lefa at cyclingnsht.blogspot.com this photo was published in a book titled Idrotten i Finlad (1906) by Ivar Wilskman. Idrotten i Finlad translates to Sports in Finland. Kaisaniemi park is in Helsinki, Finland and H.V.K. stands for Helsingfors Velocipedklubb.

Looks to me like they are playing bike polo in the street, or at the very least not in the grass.