HONG KONG — More than two dozen of Hong Kong’s young pro-democracy activists have been convicted of minor offenses in recent weeks, and some have received lengthy jail terms. Most are being put away for their involvement in the so-called Fishball Revolution, a spontaneous protest that turned violent on the first night of Chinese New Year in 2016 in the popular shopping district of Mong Kok.

On Monday, Edward Leung, the charismatic former spokesman of a young party that has called for Hong Kong’s independence from mainland China, was given a six-year jail sentence for mere skirmishes with the police. He is one of the leading figures among those known here as “localists”: activists, many of them separatists, who cut their political teeth during the 2014 Umbrella Movement.

That night in early 2016 Mr. Leung and colleagues from his party, Hong Kong Indigenous, rose to the defense of street hawkers selling fish balls and other delicacies to New Year revelers as food inspectors tried to clear them out, in front of police officers standing by. In April, during a hearing at his trial, Mr. Leung said that he had confronted an officer who was manhandling a female protester.

He was arrested and charged with attacking the police, rioting (two counts) and, a far more serious offense, instigating a riot. (He also pleaded guilty to hitting and kicking an officer.) In the end, Mr. Leung was found guilty of one count of rioting, even though witnesses say that his skirmishes with the police happened before the rioting proper even began.