University of Hong Kong student union leader Davin Kenneth Wong resigned from his position on Thursday and left the city after he reported being attacked by a man wearing a white T-shirt.

Hong Kong protesters favor black clothing, while counter-demonstrators — notoriously including gang-linked thugs hired to assault and intimidate pro-democracy activists — often wear white shirts.

Wong’s resignation letter described the attack, which occurred on August 30, as a premeditated act of violence and noted several other activists have been assaulted in a similar manner. His assailant allegedly struck him on the neck and shoulder while he was waiting for a bus, injuring his wrist when he defended himself.

Wong said he believes his life and the lives of his family members are in danger and called his departure a “one-way trip” out of Hong Kong, which he said has become a “police state.”

“I will never forgive myself for leaving Hong Kong at such a critical time, and it kills me to read the news and watch the live footage overseas. Even though it would be my lifelong shame, I was doomed to leave,” he wrote.

He wrote that leaving Hong Kong was “one of the toughest decisions I made and will ever make in my life.”

Wong is one of the student leaders who organized a classroom boycott in support of the protest movement. In late August, he called on students to skip classes for two weeks, which he said “should be enough for the government to really think through how to respond to the Five Demands.” One of those five demands, permanent withdrawal of a controversial extradition bill, was eventually granted by the city government, but the movement has vowed to continue protesting until the other four are addressed as well.

The other assaults Wong referenced in his resignation letter to the University of Hong Kong were more severe. On the same day Wong said he was attacked, Jimmy Sham of the Civil Human Rights Front, a prominent organizer of protest rallies, was assaulted by two club-wielding men at a cafe. Sham’s assistant was injured while protecting him from the blows.

The day before that, protest organizer Max Chung Kin-ping — who defied a police ban to organize a rally at the Yuen Long rail station where a hundred white-shirted gangsters attacked protesters, journalists, and bystanders with clubs in July — was beaten with metal rods by four assailants. A reporter who was interviewing Chung was also injured. The reporter was able to halt the attack by calling the police.

About two weeks before Wong, Sham, and Chung were assaulted, Chung’s friend and veteran political activist Ronald Leung Kam-shing was beaten with bamboo poles by a group of men who allegedly told him to “stop f**king stirring up trouble.”

“This is a warning. It won’t be like this next time,” the assailants said before throwing a handful of white powder in Leung’s face and departing.