A fierce street battle erupted outside the Hong Kong Polytechnic University (PolyU) on Sunday, as protesters threw bricks at police, which responded with tear gas and water cannons. The officers were trying to remove the barricades erected by the demonstrators earlier this week, and urged them to stop placing metal spikes on the roads in hopes of piercing the police vehicles’ tires.

A sergeant with police media liaison office was shot in the leg with an arrow during the standoff. The protesters have been previously filmed using bows and arrows against the law enforcement, as well as javelins, homemade catapults and slingshots.

The protesters earlier attacked a group of citizens who were clearing the roadblocks and debris outside the PolyU. A man and a woman were hospitalized with head injuries in result of the attack.

Similar scuffles occurred near the University of Hong Kong (HKU) and the City University of Hong Kong (CityU), where black-clad, masked rioters threw bricks and petrol bombs at the volunteers, who were removing the makeshift barricades.

The residents, many of whom are alumnae of these universities, have answered online calls from pro-government politicians to help clean the streets. Some of them told the South China Morning Post that protesters have gone “too far” when they switched from rioting downtown to seizing campuses and blocking major roads, including the Cross-Harbour Tunnel, which connects the Hong Kong Island with the rest of the city.

Around 50 Chinese army soldiers joined the volunteers to dismantle the barricades near the Hong Kong Baptist University, marking the first time when Beijing’s troops have left their barracks since the start of the protests this summer. The soldiers were unarmed and wore no protective gear.

Opposition lawmakers quickly claimed that China violated Hong Kong laws, which bar Beijing from deploying its military in the city unless local authorities request help. Hong Kong’s Security Secretary John Lee, however, said that the move was legal, since the soldiers were not on a military mission, but performing voluntary community service instead.