The rioters were reacting to a speech being given in Kane Hall by Trump-supporting media figure, Milo Yiannopolous.
Jessie Gamble, who is the leader of the UW College Republicans, arranged for the speech. Earlier this year, tolerant Seattle Leftists made her the target of a harassment campaign. Ironic, since Yiannopolous was banned from Twitter for alleged harassment. Almost as ironic: this was the second time since November that people have been shot at anti-Trump rallies in Seattle. The UW is of course a gun-free zone in a city that has banned gun shows, classified advertising for firearms, and driven all the gun stores out of town. There has been a massive campaign all month to ban Yiannopolous from speaking.
Seattle is well-known nationally for its violent riots and its political intolerance. It's an especially nasty example of the fruits of Leftist governance: the national leader in drug-addiction, homosexual population, and attempted suicides; one of the highest crime-rates on the West Coast, and one of the highest per capita cities of welfare recipients, homelessness, and poverty.
Yiannopolous wasn't hurt during the fracas, and finished his speech, although police locked down Kane Hall and prevented people from leaving until the Anarchists could be brought under some sort of control. The shooting victim was taken to Harborview Medical Center after police cleared protesters blocking the ambulance's path. Some others were also reportedly injured from bricks and other projectiles.
Intelligent-looking Seattle Leftists off to Protest Milo