So far it appears to be an isolated incident by one individual. An eyewitness Slog tipper writes:

Here I am smoking out the window and this anonymous looking motherfucker in a black hoodie and a backpack comes running up Denny and smashes out the windows with an ice pick or something and runs off towards Dick's. It took a half an hour before the cops even showed up. That dude was way gone before I could even call my friends over to be like 'some crazy shit is happening come look at this.'

Another photo...