An unleashed pit bull was shot and killed after the dog attacked police officers, according to Boston police. Officers were responding to a call about a fight, possibly involving a man armed with a gun, in Dorchester at about 10:30 p.m. Saturday. As police began to surround the house, the dog began running at the officers. The pit bull attacked one of them and police opened fire on the dog, authorities said. The dog died of injuries sustained from the shooting, said police spokesman James Kenneally. Two officers were taken to a hospital with minor injuries. The dog’s owner was notified; police would not comment further. Officers did not find anyone armed with a gun, officials said.