Sydney FC started its pre-season campaign with a 3-1 win over NSW Super League side Macarthur Rams, in a game that was overshadowed by crowd trouble at Campbelltown Stadium on Tuesday night.
A group of supporters among the 2,000 strong crowd chanting "RBB", a reference to Western Sydney Wanderers' fans group the Red and Black Bloc, threw two flares to spark an incident that resulted in a man and a six year-old child being injured.
A fight broke out between a group of Sydney FC fans and the WSW group in which the man was knocked out.
The child was hurt after being hit by a rock thrown by one of about 20 people involved in the fight.
Sydney FC CEO Tony Pignata, who witnessed the events, and Wanderers Executive Chairman Lyall Gorman have both said their clubs would do all they could to identify the culprits and ban them from the A-League.
"We think we know who was involved on both sides, and those guys had better think about getting Foxtel because it's the only way they're going to watch one of our games this season," Pignata said.
"It's a disgrace, an absolute disgrace, the worst thing to see when both clubs are going about trying to attract supporters the right way.
"I will sit down with Lyall (Gorman, Wanderers executive chairman) tomorrow and make sure we deal with the people responsible in the toughest way."
Professional Footballers Australia (PFA) President Simon Colosimo, who along with his team-mates was in Epping on Tuesday night at a Melbourne Heart community festival, condemned the violence.
"Quality atmosphere at games is one of the key pillars to football's success in Australia, and the true A-League fans have shown over the years how they loyally and passionately follow their teams without the need to resort to thoughtless acts that ruin the experience for those around them, including us as players," Colosimo said.
His senitments were echoed by PFA Delegate and Perth Glory Captain Jacob Burns.
"We all want passionate fans! But this violence and behaviour has no place in our game and is counterproductive to our code growing," Burns tweeted.
On the pitch, the Sky Blues fielded new signings Ali Abbas, Yairo Yau, Adam Griffiths and Fabio in the starting line-up, and it was Iraq international Abbas who opened the scoring, curling in a free-kick from 25 yards.
The two-time A-League champion went on to make it 3-0 by half-time, with National Youth League striker Nick Taneski and Dimitri Petratos both grabbing goals.
Sydney coach Ian Crook fielded an entirely different team after the break, including Croatian striker Kruno Lovrek and Nick Carle, but the A-League side could not add to its goal tally, though Macarthur did pull one back midway through the half.
Sydney FC: First half - Necevski, Dotti, O’Connell, Griffiths, Fabio, Antonis, Gligor, Petratos, Yau, Taneski, Abbas.
Sydney FC: Second half - Janjetovic, Grant, Petkovski, McClenahan, Calver, Stergiou, Carle, Lovrek, Mallia, Naumoff, MacDonald.
Kashiwa Reysol sealed its progression in the AFC Champions League with a 5-2 aggregate win over Korea Republic club Jeonbuk Motors.