Battle of the blues Recently, I spoke with retired NYPD Detective Tom Smith, who was on the Joint Terrorism Task Force, three decades with the NYPD, specialist on narcotics and gang warfare. I asked him about this snowball incident in Washington Square Park last week — people pelting cops — what should we do if comes more snow and more hooligans? Smith: “NYPD leadership gets in front of a camera. Says I want 20 people arrested on the scene. Cops can not be assaulted. Someone’s calling additional units to get there and lots of people go to jail. “Criminals know the policies of how…