a peaceful bike ride is violently disrupted, and it's all caught on camera by one of the stunned riders. february 9th, 2011, a friday night in puerto dellegre, brazil. bike riders are taking part in critical mass, an event with a single purpose, to promote bicycling as an alternative to driving. in countries around the world, bicyclists get together once a month for solidarity. >> bikers fight the power all the way down. >> most critical mass rides are peaceful, not this one. livia and elton are two of the riders. >> i go to the march every day -- every month.