CYCLISTS IN urban centres around the world have been losing moral ground over their erratic and morally superior behaviour. But nowhere have confrontations between drivers and kids on wheels resulted in an open declaration of war - except San Francisco. Critical Mass, an independent- minded bunch of non-toxic transport supporters, used to spend one Friday evening a month creating gridlocks in the rush-hour traffic. In summer, the monthly ride has escalated from a "happening" which used to block a little traffic, to a moving army. Imagine several thousand youths on bikes, free-wheeling through the city, harassing motorists, controlling the streets. The Wheeled Ones are holding the town to ransom.

There has been even a confrontation with a maverick law enforcer, Mayor Willie Brown. Accusing the cyclists of behaving as though they were above the law (a sentiment which drew vocal support from car drivers), he announced a police crack-down on Critical Mass, but hastily ditched the heavy-handed tactics when he saw what he was up against. These are self-righteous Rebels with a Cause. This was all in the course of the month. By the date of the next meeting, both positions were suitably entrenched.

So, last Friday week, Down by the Waterfront, more than 5,000 cyclists gathered at Justin Herman Plaza. There's a music fest atmosphere, the faint scent of a spliff and a DIY sound system. The cyclists have been joined by hundreds of roller-bladers, who definitely represent the far side of this event - a woman in a black, lace babydoll nightie glides by. Her partner is wearing a gas mask. The bladers are having their own party: the Midnight Rollers. "Six more wheels on that bike and you can come hang with us," intones the DJ. I can relate to that. Cyclists can be so morally uptight, it would be like inviting a bunch of vegans to the barbecue. Plus, Brando would never have worn Day-Glo shorts and one of those pointy, aerodynamic helmets.

But back to the plot. To the accompaniment of shouts of "shut up" and "let's ride", the throng moves past Willie Brown, still mouthing political platitudes into a microphone. Immediately, they ditch the officially approved route. By nine o' clock I am sitting outside Vesuvio's on Columbus watching cyclists whiz through red lights, drivers sounding horns, fingers in the air, police helicopters overhead tracking renegade bands through the city. Critical Mass is proudly leaderless, and this is the kind of anarchy the Beat Poets, who favoured Vesuvio's, would doubtless be proud of.

All in all, there are 250 arrests and scores of fights as car-drivers literally attack cyclists. At Jones, tram passengers jump down and kick a protester's bike; on Franklin a woman at an intersection grabs hold of the speeding cyclists and shouts: "Red light, you've got to stop." Drivers everywhere shriek obscenities from besieged vehicles.

From the poor, beleaguered police captain came this response: "I sensed hostility... an unco-operative attitude." And the verdict from Critical Mass? They plan to do it every day. I'll keep you posted. From Hollister, goodbye.