From what we can tell, the hoop monster in question was a part of Seattle's May Day protests. Or at the very least, he was using the day as a chance to go all Monstars on the hoop. The Seattle Police Department had a good sense of humor about it at least:
File this one under the Tumblr "~~Just Soccer Hooligan Things~~". It's such a bummer when you mean to drunkenly assault a police officer and instead drunkenly assault one of your other drunk fans because SPORT.