Cars honked as they drove past the hotel, on which someone had written “torture chamber” in chalk. Children raced around trees and juggled soccer balls even though it was almost 11 p.m. As scores of young people began to interlink their arms and dance in unison, a group waved and shouted at the window where they thought Djokovic was staying. In fact, the tennis star was in another part of the building, unable to see the park, police officers said.