Did they legally rent the road and land from the city so that it in effect becomes "private" property?
Is the event free and open to the public?
Did they and the city follow all the regulations in the Brown Act in terms of mandatory public notice of plans and hold public meetings to discuss this group renting the street?
We went through a similar battle and won in Manhattan Beach last year and this year, read up on it here:
http://southbayopencarry.org/2010/09/ (that's just the September page, there are articles on it possibly on the august page as well as the october page for 2010.