Police have fired a plastic bullet after being attacked by a crowd of more than 100 loyalists throwing missiles in Carrickfergus, County Antrim.
Fireworks, petrol bombs and rocks have also been thrown at officers in the Cloughfern area of Newtownabbey.
The violence came as union flag protests again caused traffic disruption in Northern Ireland.
They began in some areas at 15:00 GMT and took place in Counties Antrim, Armagh, Down, and Londonderry.
Many arterial routes in Belfast were blocked by loyalist protesters angry at the decision of Belfast City Council to restrict the flying of the union flag from Belfast City Hall.
A bus was set alight near the Rathcoole estate in Newtownabbey.
So far there have been no reports of violence in Belfast.
Police used water cannon on the Shore Road in Whiteabbey and it was also deployed in Newtownabbey.
There have been 39 days of protests over Belfast City Council’s decision to fly the flag on designated days only.
Translink withdrew all its bus serivces in Belfast, apart from Falls Road services and buses to Belfast International Airport.
Police said that due to ongoing protests, access to Ravenhill stadium for the Heineken Cup pool match between Ulster and Glasgow was difficult.
Thousands of supporters encountered delays.
There were also protests in Glasgow and in Liverpool at 18:00 GMT on Friday.
Operation Sit In
Meanwhile, people used social media to initiate Operation Sit In – a counter to the protests that has encouraged people to come out regardless and support their local pubs or restaurants.
Stephen Magorrian, the managing director of Botanic Inns, said people could have a great night out in the city centre.
“There is great entertainment, so stay in the city. We need the support.
“Things are still going and we have some of the best restaurants and bars, but if we don’t support them we will lose them.”