Brazilian police are questioning a man who drove his car through a crowd of dozens of bicyclists, injuring at least 16 riders who were taking part in a group ride to raise awareness of cyclists on city streets.

The driver of a black Volkswagen accelerated as he drove through the center of a pack of riders in the monthly Critical Mass bike ride Friday evening, in the southern city of Porto Allegre. More than 100 riders are believed to have been participating in the event.

Several participants and bystanders recorded the incident, in videos that have now made their way online. The graphic footage shows people being tossed aside, even as some riders lay across the hood of the car after being struck.

According to the blog The Urban Country, the driver, identified in several reports as Ricardo Neis, 47, told police Monday that he had acted in self defense.

Here’s a video of the incident currently on YouTube — and a WARNING: it’s a graphic, closeup view of an event going from peaceful to tragic in mere seconds, around the :50 mark:

Neis reportedly had his son, 15, in the car with him when he sped through the crowd of cyclists. Moments after their car ran through the pack of riders, the pair abandoned the vehicle.

On Monday, Neis, who works at a bank, and his son said that cyclists had begun hitting their car, a VW Golf, according to Zero Hora.

Five cyclists who were hit by the car disputed that claim when they spoke with police early Monday, saying they were only calling for calm on the street.

And Zero Hora reports that one rider said that it was actually fortunate that it rained on the day of the ride.

Eduardo Fernandez Iglesias, who required stitches in his head after being struck, said that if the weather had been better, more children — like his own daughter, 9 — would have come along for the ride, as well.

The incident has sparked outrage among activists and riders, who say that events like Critical Mass are meant to show that cyclists don’t need a special dispensation from traffic officials to use the streets.

In recent years, there have been other conflicts between cyclists and motorists at Critical Mass events. Some of them are compiled on their own Wiki page. Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.