FOR TWO MATCHES a year, Western Australia comes to a grinding halt.
You're either a West Coast fan or a Fremantle supporter, there is no in between.
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(Unless for a somewhat bizarre reason, you've elected to barrack for a team based on the east coast, a choice usually frowned upon.)
It's friend against friend, neighbour against neighbour, and in some particularly fraught situations, family against family.
But Saturday will add a new chapter to the fierce rivalry, when the very first AFLW Derby is played out in the vast arena of Optus Stadium.
Fremantle is now in its fourth season of the NAB AFLW competition and will be facing off against newcomer West Coast. It's a reversal of the men's roles, where the Dockers joined the AFL eight years after its state rival.
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East Fremantle WAFLW premiership coach Nikki Harwood has seen the development of the women's game in the state progress over the years, having played and coached at state level since 2004, and always felt the Derby would have a new chapter.
"Since the start of the AFLW and seeing the expansion, there was no doubt we were going to see one. We just didn't know when," Harwood said.
It's a massive rivalry, and they're two very one-eyed supporter bases. No one sits in the middle. So, when it's on, it's on
"You're either one or the other, it's a bit like living north or south of the (Swan) river. I live on the south side, so people who live in the north are a bit strange," she finished with a laugh.
The only previous iteration of a women's "Derby" was a handful of years ago, when the state academy took to the field.
"They split the talent academy in half and put them in club jumpers," Harwood said.
"That was more to show the support of the Eagles and the Dockers, and they called that the first Derby, which it wasn't, really."
Two debutants will have a baptism of fire, with West Coast's Kate Orme and Fremantle's Bianca Webb coming in for Ashton Hill (ACL) and Mia-Rae Clifford (omitted) respectively.
In all, seven former Fremantle players will take to the field in the blue and gold, while the five-team WAFLW competition played over winter ensures most players already know each other well.
We're unlikely to see the Eagles thump the Dockers by 85 points, as was the case in the first AFL Derby in 1995.
But regardless of the result, after making its AFLW debut against Collingwood at Vic Park, West Coast's first home game will be one to remember for a proud footy state.