Yeah, not sure what you do to stop that. I did notice the woman cyclist at the end said something to him, and then started to dial the phone. Way too late to do anything at that point though. He looked like a pretty big guy, not sure who there was going to confront him. Certainly not the mom with the stroller, who knew something was up and got the heck out of there...
Even if one of them called 911, not like the SFPD would have responded in time.