Fans have reacted with disgust after footage emerged showing a man in a Dublin jersey kicking a homeless man in the head.
The video was posted on social media and has since gone viral and been shared more than 2,000 times.
Gardai are investigating the incident, which happened at around 6.30pm in the Parnell Street area on Dublin's northside.
It happened as crowds dispersed from Croke Park after Dublin's All-Ireland win.
A witness told the Herald he heard "shouting and roaring" on his way home.
"People were shouting trying to stop the man and he was shouting back," he said. "He just kept kicking your man. I wasn't even thinking about it at the time.
"I just seen him getting kicks in the head."
He said the victim, who had been sitting in a doorway, remained on the pavement throughout the attack.
"He didn't get up off the ground. He got a couple of boots to the head."
A number of Dublin supporters then stepped in to try and protect the victim from the blows.
Local councillor Gary Gannon condemned the shocking attack and said it did not represent the wider Dublin community who turned out to support the Boys in Blue at the weekend.
"I was disgusted to see the video," he said.
"The guy that carried out that attack doesn't represent the people of Dublin."