Police blasted water cannons Wednesday at protesters in Northern Ireland who set small fires and hurled bricks, rocks and bottles at them during a second night of violence over a brutal stabbing on a Belfast street. Demonstrators wearing masks tore bricks from the walls outside homes and smashed sidewalks with sledgehammers to toss at riot police. In one place, the unruly crowd used sections of a dismantled picket fence to take cover on the street.