We cannot see the hands of the fashion-oriented side in that photo. Other photos from the incident show pepper spray and other things being shot past similar shields, so I would not assume their hands are empty.
Furthermore, the shields themselves are quite lethal weapons. I study HEMA, and in almost every shield+weapon system the shield is not a passive protective device, but is used as a *very* effective impact weapon. The edge of the shield is particularly troublesome.
Any thoughts on the body language displayed by the onlookers and the participants themselves?