More than 30 people have been arrested after another night and day of violence centred on a new Tesco store in the Stokes Croft area of Bristol.
Avon and Somerset police said officers suffered head, neck, back and leg injuries, and claimed more arrests would follow once CCTV footage had been studied.
During last night and into the early hours of this morning, protesters armed with rocks and bottles clashed with police in riot gear.
Local protesters against the Tesco Express insisted the violence was caused by outsiders.
Chris Chalkley, of the People's Republic of Stokes Croft, which has been lobbying against the Tesco, said he had been hit by a police baton and saw others being struck.
But hesaid: "People were coming from afar for a ruckus. I didn't recognise many of them."
Violence first broke out over the store last Thursday and Friday and police allegedly found petrol bombs in a nearby squat. The Tesco remains boarded up.
Demonstrators had gathered peacefully in Cheltenham Road to show opposition to the supermarket at 9pm on Thursday, playing music and dancing in the street.
Police said a "good-spirited" evening turned sour when some protesters armed themselves with rocks and bottles and splintered into smaller groups.
They claimed numbers swelled to more than 400 as trouble flared. A spokesman said: "A group then splintered off, some donned masks and armed themselves with rocks and bottles, and started heading towards the city centre. Neighbourhood officers tried to speak to them but the crowd responded by pelting police with missiles. Officers had to withdraw and seek support from colleagues wearing protective clothing."
During the morning there was a tense stand-off between police and the three protesters who had climbed on to the roof of the three-storey Telepathic Heights. Witnesses reported that roof tiles and concrete blocks were thrown towards police. A negotiator went on to the roof and handed them water. Cheers rang out from onlookers after police arrested them.
Stephen Williams, the Lib Dem MP for Bristol West who saw the chaos, said: "These protests have been hijacked by extreme leftwing groups. They do not represent the views of the people in this area. A lot of people were angry about Tesco. But there is no place for this violence."
An amateur photographer Milo Sweet, 35, said: "Police came charging down the road with their batons that's when most of the crowd got angry and the atmosphere changed.
"They had stopped wearing their rounds hats, put on their riot gear and just charged. I got hit by a riot van and a police horse. The police were trying to move us to a place where bottles were raining down."
Another witness, Richard Ayres, 39, said: "We were shoved back by riot police with helmets, shields, truncheons and dogs. I received three blows to my legs and a blow to my head for which I have received hospital treatment.
Assistant Chief Constable Rod Hansen, of Avon and Somerset police, said investigators were now combing CCTV footage to try and identify more offenders.
He said: "A number of protesters were clearly intent on inciting trouble. This included breaking down residential walls and removing roof tiles to use as missiles, lighting fires, setting up barricades in the road and daubing graffiti throughout the area."
A Tesco spokesman said: "This is not an anti-Tesco protest, our store is not even open."