Western Sydney Wanderers face hefty punishment over the  offensive banner their fans displayed during the Sydney derby after Football Federation Australia issued the club with a show-cause notice on Monday.
The governing body said the display, which depicted a blue-faced man resembling Sydney FC coach Graham Arnold performing oral sex, was "offensive to any reasonable member of the public". Â
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Wanderers finally turn tables on Sky Blues
A first-half goal to Brendon Santalab proved to be enough for the Western Sydney Wanderers to finally crack Sydney FC after 20 rounds, as the black and red handed the Sky Blues their first loss this season in a 1-0 win.
The banner has been widely condemned as homophobic. Sydney FC have requested a formal apology on behalf of Arnold and his family.
Fans in the Wanderers end held the "tifo" aloft for several  minutes in front of the near 45,000-strong family-friendly crowd before it was eventually forced down by security. Fans group the Red and Black Bloc  saluted the banner on social media after the game.
It's understood the Sky Blues have told FFA they want the Wanderers to apologise to their coach. The governing body is likely to come down hard on the club, which has already been in strife over fan behaviour and is sweating on a suspended points deduction over flare-lighting and other anti-social activities.
A hefty fine and  restrictions on the RBB loom as possible sanctions, as A-League bosses attempt to drive home the message  that the fan base has "abused the privileges afforded to active supporter groups".
The incident overshadowed Western Sydney's first derby win in more than three years, which was also marred by crowd violence and misbehaviour leading to 15 arrests, both inside and outside the stadium.
The Wanderers have until midday on Thursday to respond. Â The club released a statement on Sunday pledging commitment to providing a family- friendly environment at games.
![At the centre of the storm: A cropped section of the offending banner.](/web/20170222180934im_/http://www.smh.com.au/content/dam/images/g/u/g/a/q/y/image.related.articleLeadwide.620x349.guh4rr.png/1487774278947.jpg)
Striker Brendon Santalab, who scored the winner in the 1-0 result against the ladder-leading Sky Blues, says poor crowd behaviour threatened to take some of the gloss off the game where they ended a three-year derby drought.
In a statement on Monday, the A-League club said it doesn't want misbehaving fans at their games and Santalab says they want to focus on a nice family environment.
AAP