A group of teenagers armed with baseball bats and machetes attacked Australian teachers and students on Monday, injuring 18 people and forcing a high school in Sydney to be locked down, police said. Five youths barged into the morning assembly at Merrylands High School in south-west Sydney, witnesses said, grabbing students before starting to smash windows at the school. The school then locked its students in classrooms as the youths, who were not students, went through two school buildings, smashing more windows and equipment, police said. "They caused a considerable amount of damage," a police spokesman told reporters. "There have...