The Supreme Court has declared it's cool with cops engaging in retaliatory arrests… just as long as they have the probable cause to do so. Given the thousands of obscure laws we've been cursed with by legislators, most law enforcement officers will be able to find someway to shut up someone by putting them in cuffs. (Whatever they're wrong about can be salvaged by the good faith exception.)
In this case, plaintiff Russell Bartlett was arrested after not talking to police and telling other winter festival attendees to not talk to the police. The officer who arrested Bartlett claimed Bartlett was drunk and disorderly, hence the supposedly-justified arrest. Here's the background, as summarized in the Supreme Court's opinion [PDF]