Tens of thousands counterprotesting a rally purporting to be about free speech swarmed Boston on Saturday, leading to a few conflicts with police and widespread attention from traditional and social media.

A total of 33 arrests were made Saturday in Boston, primarily resulting from disorderly conduct and from alleged assaults against police officers, the Boston Police Department said. Police indicated that some demonstrators were throwing rocks and bottles of urine, but that did not represent the majority of participants, according to Police Commissioner William Evans.

"99.9 percent of the people here were for the right reasons" and participated peacefully, Evans said.