A female pool player clapped and cheered as she forfeited the final of a tournament in protest at having to play a trans woman.
Lynne Pinches refused to play her opponent Harriet Haynes at the Ladies Champions of Champions event in Denbighshire, Wales.
Footage shows the player approaching the referee to inform them of her decision to forfeit the game and wave goodbye to her chance of winning the tournament.
She then went back to her seat, packed up her cue, and left the arena as a stunned audience watched on.
Her bemused opponent was then left to pick up the trophy by default.
Pinches' brother, Barry, took to social media to praise his sister for 'taking a stand' and voiced his opinion that it was 'unfair' for her to be drawn against a trans player.
'Full credit and great respect to my sister Lynne Pinches yesterday for taking a stand and not playing in the biggest match of her pool playing life because she feels it's so unfair to have to compete against a trans woman,' he said.
'I completely agree with her view that it is unfair to expect women to compete against trans women in pool or any other sport for that matter.'
Pinches had been among a host of top female players to speak out over transgender women being allowed to compete against them in elite competitions.
The controversy now rocking the top levels of women's professional pool began on October 24 when the sport's international governing body, the World Eightball Pool Federation, changed the rules over trans players' participation in female tournaments.
Initially, in August, with increasing numbers of trans players applying to play in women's tournaments, the WEPF had put out a joint statement with its main sponsor the Ultimate Pool Group ruling that 'these events will be exclusively open to individuals who are born female.'
But just eight weeks later there was a shock reversal in this decision, which several women players have suggested was made under pressure of legal threats from trans competitors.
The WEPF and Ultimate Pool issued an update on 'competition eligibility for transgender and non-binary players' stating that there would be no discrimination on the grounds of gender identity.
They stipulated that they would operate a gender 'self-identification policy' for competitors, but added that they reserved the right to test that testosterone had been suppressed to the levels required of trans athletes by the International Olympic Committee.
Within a week of this announcement, more than 60 professional female pool players joined forces through a WhatsApp support group to oppose the changes, the Mail on Sunday was told.
After his sister's walkout on Sunday, Barry said that the sport would look back in years to come and conclude that it is 'grossly unfair on women who have practiced hard and are competing in their chosen sport'.
Barry added: 'For the record, this post is about fairness in women's sport, that is all. I have no problem whatsoever if somebody wants to ide