A protestor throws back an exploded tear gas shell at police officers in Hong Kong, Saturday, Aug. 31, 2019. While other protesters marched back and forth elsewhere in the city, a large crowd wearing helmets and gas masks gathered outside the city government building. Some approached barriers that had been set up to keep protesters away and appeared to throw objects at the police on the other side. Others shone laser lights at the officers. (AP Photo/Kin Cheung)