It followed a similar incident also in the ALM less than 24 hours earlier. Police ejected 14 people and the Western Sydney Wanderers fan group the Red and Black Bloc (RBB) staged a walkout on Saturday night at CommBank Stadium.
A group of approximately 30 to 40 supporters who sit in The Den seats at the northern end of Suncorp Stadium left in the 25th minute, just after forward Marco Rojas scored the opening goal.
Video of a push and shove by fans with police was earlier posted on social media site X. An officer can be heard to say "that sort of behaviour will not be tolerated".
The Den entered the ground and AAP has been told they alerted Roar officials of their intention to walk back out. AAP has sought comment from the Roar.
The Australian Professional Leagues (APL) confirmed to AAP they were investigating a first-half incident in the Sydney derby.
Sydney FC won the derby 4-1 but by half-time the RBB had exited the stadium.
The Wanderers said they were "very concerned" about an incident they said occurred in the 10th minute and were conducting a review.
"In what should have been the club's biggest night of the season in front of a sell-out crowd, an incident has triggered a mass walk-out by the club's passionate active supporter group," the club said in a website statement.
"The safety of Wanderers members and fans is of the utmost importance to the club."
NSW Police released a statement saying spectators had earlier gathered at Prince Alfred Park and marched to the stadium, during which several flares were ignited and two people were refused entry.
Police had then assisted security at approximately 8pm after a fight broke out on the concourse area of the stadium. There were no reported injuries.
A 37-year-old man was ejected and issued with a ban notice and the RBB had walked out in support of him.
"As a result of the police operation, 14 people were ejected, six of which were issued banning notices," said the police statement.
"Two people were issued an infringement notice, one for offensive behaviour and a second for igniting a flare just before full-time.
"Inquiries continue with further action expected in relation to the possession and igniting of flares before and during the match."
A lit flare could been seen in a bay containing Sydney FC supporters.
A lit flare is seen during the ALM derby clash at Commbank Stadium. (Dean Lewins/AAP PHOTOS)
Various reasons have been given by fans on social media site 'X' for the RBB walkout.
There was widespread discontent with a "heavy-handed" police response, with one supporter saying the police action was taken because "they (RBB) tried to go back into the bay after holding banners in other bays".
Another suggested there was dissatisfaction with the officiating.
Police said they took action to "ensure the safety of players, officials and thousands of spectators attending an A-League match".
An (APL) spokesperson provided AAP with a statement.
"We are aware of an incident that occurred inside the stadium during the first half," the spokesperson said.
"We are working with all parties to investigate the matter as part of prescribed protocols."
The Wanderers said they were "working through numerous complaints and waiting to receive further information from several key stakeholders about the incident to determine the facts.
"The club is committed to doing a full review of the incident and will provide further updates in due course."
Sydney FC declined to comment.
