One rider's account of the incident:
This was towards the end of the ride (after splitting off and dissipating). We had about 30 people by the time we were leaving Japantown when I heard a noise, which I could even hear over the music, and I turned my head to see a minivan on my left just having run over a bike and saw the rider on the ground. Riders nearby yelled at the driver to stop and the minivan just sped away. Many people in the ride chased after the van and surrounded it after catching up with it at the red light. The driver had her hand pressed on the horn the entire time. The cops got there pretty much right away as they were following right behind us. I rode away with the rest of the ride but some people stayed behind to deal with the cops. I didn't see the rear window get smashed but I can say that I only saw the couple sitting in the front of the minivan as the rest of the windows were heavily tinted and we could not see that there was anyone else in the vehicle.
The driver's response to the idea that she had hit a rider was "that's ridiculous."