Snowball fights, like marijuana smoking, have always been lawful on private property, as long as the results don't go public. The reason government wins in court battles, is because most private citizens don't know how to fight legally, and most attorneys can't be on their side. Attorneys work for the courts first, for the State second, for themselves third, then maybe for their client, who is legally a ward of the court. See what Corpus Juris Secundum has to say at vol. 7, sections 2 and 4: http://www.gemworld.com/US--AttorneyClient.htm.