On 18 April 2020, Leung was arrested as one of 15 Hong Kong high-profile democracy figures, on suspicion of organizing, publicizing or taking part in several unauthorized assemblies between August and October 2019 in the course of the anti-extradition bill protests. Following protocol, the police statement did not disclose the names of the accused. A day prior to his arrest, he was stabbed with a sharp object while demonstrating in solidarity with pro-democracy legislator Dennis Kwok, who had been strongly criticized by the pro-Beijing camp. The attack happened in front of the Liaison Office and he was helped by fellow activist Raphael Wong before being moved to a hospital, where he was later discharged at his own request. In September 2020, the 83-year-old man who stabbed him went on trial for the attack and was controversially praised by the magistrate for "loving society". The elder man was also quoted as saying he wanted activists Joshua Wong and Ted Hui "to die as soon as possible", and included Leung in the same wish.