BYOBW - "Bring Your Own Big Wheel" race (San Francisco).
This is a free and unauthorized event. People race with Big Wheel toy tricycles and other non-motorized vehicles down the steep and curvy segment of Vermont Street in Potrero Hill. The racers reach dangerous speed and frequently crash. This race used to take place on the famous curvy segment of Lombard St, but because some of the Lombard St residents did not like the event and asked the police to shut it down, in 2009 they moved the BYOBW race to Vermont St where the neighbors have a more positive attitude.
I shot many of those photos with a very slow shutter speed to capture the motion effect. It is not easy to get good shots of this event.