A Moscow court on Wednesday sentenced a man to four years in prison for punching and kicking two police officers at an unsanctioned protest against corruption, the Kommersant newspaper reports.

Andrei Kosikh is the fourth protester jailed for violence against police at rallies on March 26 that drew thousands onto the streets in cities across Russia calling for the resignation of Prime Minister Dmitry Medvedev.

The protests were organized by Alexei Navalny, an opposition politician who gained popularity after publishing exposes of corruption by senior officials including Medvedev. He intends to run for president in elections next year, despite a criminal conviction in a case widely considered to be politically motivated.

Prosecutors requested a four and a half year jail term for Kosikh, saying his attacks had caused a head injury to one officer and physical pain to another, according to Kommersant. Kosikh pleaded guilty to the charges.

His mother told the court her son hit the officers after seeing them beating a woman. “He doesn’t understand himself how it happened. He’s a very emotional person, he couldn’t even harm a cat,” she was quoted by Kommersant as saying.

More than 30 people were jailed for violence against police officers at a protest in Moscow in May 2012. The convictions stifled a wave of protests that followed alleged rigging of parliamentary elections in 2011.