A community has had, for many years, a parade down the middle of its downtown, to mark the Feast of St. Sebastian. Many who attend seem to think that this is an opportunity to engage in public consumption of alcohol. Towards the end of the parade, a group suddenly jumps into line, holding a banner that says "Snipe hunting is animal cruelty!" The feast of St. Sebastian has nothing to do with snipe. People along the parade route suddenly swarm the street. Local law enforcement sees that violence could erupt, so it grabs the half-dozen or so people holding the banner, and hustles them off to a waiting police van. They are held for a few hours, until the crowds disperse, and then are released.
These people want to sue for a violation of their Federal civil rights. Will local law enforcement be able to escape liability by using the defense of privilege? Why or why not? Will local law enforcement be able to escape liability by using the defense of immunity? Why or why not?