Trouble flared after Derry City’s defeat to Shelbourne last night.
Police said they are investigating incidents before and after the game at the Brandywell.
Flares were set off ahead of kick-off.
On the pitch, Shelbourne won 1-0 to secure their first League of Ireland title since 2006.
However, the violent scenes marred the celebrations.
Derry City & Strabane Chief Inspector Luke Moyne said: “Just before kick-off, a number of flares were set off by both sets of fans.
“As the game finished, violent scenes took place inside the stadium which were followed by further disorder outside the stadium. The area is now calm and a policing operations remains in place.
“Thankfully, there were no reports of any serious injuries. As part of our investigation into tonight’s disorder, footage obtained by our evidence gathering team will be used to help to identify those offenders.”