The 2019 Yuen Long attack, also known as the 721 incident, refers to a mob attack that occurred in Yuen Long, a town in the New Territories of Hong Kong, on the evening of 21 July 2019. It took place in the context of the 2019–2020 Hong Kong protests. A mob dressed in white stormed the MTR's Yuen Long station and attacked protesters returning from a demonstration in Sheung Wan on Hong Kong Island as well as bystanders.
Despite over 24,000 calls to the 999 emergency hotline, the police arrived 39 minutes after the attacks and one minute after the mobs had left the station. Around 30 non-police tactical unit trained police officers were assigned to standby at Tuen Mun Police Station for contingency. At least 45 people were injured in the incident.
The government condemned the violence. There was widespread criticism of the police for its poor response to the incident and disputed narrative of the events. As of September 2022, eight assailants have been convicted. Attacked passengers and protestors were later charged with riot as well, with at least one found guilty. As of April 2025, 21 people have been convicted for rioting over the attack, 13 of whom belonged to the white-clad group and the remaining eight being other people at the scene; seven of the latter have appealed their convictions and sentences.