A few months ago, while Walter was doing one of his counter-protest things, that guy in the back ran up and threw some kind of apparent bomb into the crowd and ran off. Professional Douche (another YouTuber doing similar counter-protest content) was also there, and both he and Walter caught it on camera.

My recollection is that the device was a dud, and didn't explode or hurt anybody, and that the suspect (and potentially an accomplice) were soon apprehended a block away.