Shitting in the town well is an act of aggression against the entire town. So is wanton neglect that causes a mauling. So the normal case of operation in a libertarian based societt would be to charge the responsible party with the crime against the injured party. Find evidence to support that claim and then convict them in a court of their peers.

Most people don’t understand that libertarianism is a double-edged sword or rather that it should be applied as such. You’re free to do what you want, but you’re not free of the consequences of your actions.