Gardaí from across Dublin were called to deal with a riot involving around 100 football supporters before a high-profile League of Ireland fixture last Saturday.
The riot squad was sent to deal with the fans of Shamrock Rovers and Bohemians after they clashed close to Rovers' Tallaght ground at around 7pm last Saturday.
Gardaí said a large group of Bohemians fans went to Tallaght on the Luas and clashed with dozens of Rovers fans near the stadium, with scuffles and bottles being thrown. Four people arrested for public order offences.
Gardaí said they were concerned that many of those involved had travelled over from Glasgow and Cardiff intent on causing trouble.
Gardaí from across the city rushed to help local gardaí in Tallaght who were struggling to separate the two groups of rival fans.
Shamrock Rovers, Bohemians and the FAI all gave differing accounts of the incident.
A spokesman for Shamrock Rovers said a group of between 100 and 150 rival Bohemians fans descended on the Tallaght ground without match tickets and that the club's fans had no known involvement.
"From my understanding a group of Bohemians supporters made their presence felt and the guards did their job," he said.
However, according to Bohemians, gardaí had to form a line between the rival fans after a group of up to 60 of their supporters encountered Shamrock Rovers fans who had come out of a nearby hotel.
"Our fans came down from the Luas station; there would have been about 50 or 60," he said. "The Rovers fans were in the hotel across the road from the ground. They heard the Bohemian fans and they came out and there was a line of guards in the middle. There was a bottle thrown and it hit a Bohemians fan but he wasn't hurt, thankfully.
Joe McGlue, chief security officer for the FAI said: "The fixture passed off without any major incidents either inside or outside the stadium." He explained that a "potential incident" on the Belgard Road was averted thanks to the efforts of gardaí.
"There was an attempt to clash by a small amount of individuals related to both clubs on the Belgard Road [but] this was dealt with within seconds by members of An Garda Síochána. The Belgard Road is a good distance from the stadium," he said in a statement.