The city is cancelling all large-scale events, including any in the Castro District or at AT&T Park.
San Francisco is promoting a 'Home for Halloween' campaign to prevent the kind of violence that's broken out in the Castro in recent years.
In 2006, nine people were shot. Not many people showed up at last year's party at AT&T Park - so that too has been scrapped.
BART and Muni are not planning to provide extra service.