Students that were on college campus at the University of Pittsburgh inside a building observing the riots at the G20 summit were trapped and attacked with tear gas. As far as I can tell from the video the students were not doing anything to provoke the attack or the containment.

There are some obscenities in the following video, and although there are other links attached to this video, this is the only one in which we see the actions of the police were in question:

This was not the only reported incident that night.  According to the Pittsburgh Post-Gazette, riot police chased students who were waiting in line at a local restaurant, studying at the library and observing in front of residence halls. And the Student Press Law Center reported that riot police also targeted and arrested journalists as they attempted to document the event. In short, throughout the entire event there were 190 arrests made, 51 of those being University of Pittsburgh students.