Two groups, believed to be Linfield football supporters and Armagh GAA fans, were involved in an altercation at Portadown Train Station on Saturday night.
In a statement, police confirmed they had received reports of an incident and are investigating.
Linfield had lost 3-0 to Portadown at Shamrock Park in the Irish Premiership while Armagh were defeated by Donegal in an All Ireland quarter-final at Croke Park.
The police said, “At approximately 8.40pm on Saturday, August 9, police received a report of an altercation between two groups at a station in the Woodhouse Street area of Portadown. When police attended a short time later, there were no ongoing incidents.
“An investigation is under way to establish what occurred.”