Walking through Civic Center Plaza on Friday at lunch time, I saw the huge set-up for the Dew Tour.
Events hadn't officially started, but BMXers were practising their stunts on a course that allows them to get airborne at least 3 times.
Fences were just coming down around the skateboard course, which was relatively flat & seemed to be about obstacles rather than half pipes. Like the cyclists, the boarders were exclusively skinny young men.
There's a stage & a corporate village of warehouse-sized structures. Plenty of Civic Center's street people mingled with the spectators. SFMike has more. The event is free.
§ The Dew Tour October 18 - 21, 2012 Civic Center Plaza, San Francisco
§ Freestyle Events October 21, 2012 Harrison Street, between Fremont and Spear