Mouncey is the transgender woman whose eligibility for the AFLW draft was denied by the AFL this week, despite the fact that she meets one of the International Olympic Committee's technical criteria for being a woman and despite having played, and continuing to play, in the Canberra women's Australian football competition. Mouncey is far from the first trans-woman athlete to seek inclusion in female competition, but she belongs to a gathering movement that will keep exposing the unreadiness of sporting organisations until satisfactory definitions of eligibility are reached, understood and accepted.

Sport is uniquely unprepared for situations that escape binary division. The goodwill is present, against a societal backdrop where the remnants of bigotry, needing no extra oxygen, do everyone else the great favour of public auto-erotic asphyxiation with claims such as that athletes like Mouncey "decide" to switch gender so that they can be stars. Er, yeah, what man has not considered becoming a woman so he could enjoy the riches and superstardom of playing women's sport?

A more tolerant future is coming; you only need to listen to a wide enough sample of children and teens to believe in that promise. While most sporting authorities are keen to position themselves on the right side of history, the Mouncey case demonstrates that sport's own definitions - its segregation into two gender categories, and its inherently competitive basis - remain intractably either/or, win/lose and yes/no amid a real world that is shaking itself free from the binary. Because of this inbuilt two-sidedness, sport may take longer than other parts of society to catch up.

Mouncey is a former champion handballer. As Cullen Mouncey, she represented Australia in that sport before beginning to transition in 2015 and 2016. Handball has granted her eligibility to play as a woman, but Mouncey wishes to play Australian rules, and has competed for the Ainslie club in the ACT. Her coach, Chris Rourke, has reported no complaints from fellow women competitors; rather, it is sideline observers, mainly men, who have commented on Mouncey's size and questioned the fairness and safety of her being on the field with other women.

In applying for the AFLW draft, Mouncey presented a blood testosterone level that is legal by IOC standards but had yet to meet a second IOC criterion, which is that the person identify as female for four years before being allowed to compete. The AFL did not, however, rely on that. In an opaque decision, the AFL has reportedly cited Victoria's Equal Opportunity Act, deciding that Mouncey's "strength, stamina and physique" are so superior to other players' that it is legal to discriminate against her. Doubtless, the league is also concerned about safety for smaller footballers.

Although the natural inclination is to admonish the AFL - how can Mouncey be safe to play in one women's competition and not another? How can the IOC's clear definition be ignored when it is the only measurable standard that exists? - you can see where the league is coming from. Its problem is that Mouncey might, at this stage of her transition, be a little too powerful on the football field.

This is why competitive sport cannot easily handle athletes of transitioning or indeterminate gender: in plain English, because if they are too strong, their presence is unfair to other women athletes. My friend Cate McGregor was welcomed into women's cricket, up to a point, because Cate (who will I hope forgive me for this) was not threatening to be the next Meg Lanning or Ellyse Perry. But if David Warner or Patrick Cummins became women, different story.

The pro-inclusion body Athlete Ally has argued that this judgment is a form of prejudice that is applied to transgender athletes and not others. Nobody else is rubbed out of sport because they might be too strong. It's impossible to dispute: this is a very particular targeted prejudice. But does that make it necessarily wrong? How can any form of gender-based exclusion ever not be wrong?

Gender ambiguity: South Africa's Caster Semenya escaped easy definitions. Photo: AP

Athletics has battled with this for Caster Semenya's entire career. Semenya's gender ambiguity is different, but the upshot has also been sport's struggle to balance two types of fairness. Sports are artificially divided into men's and women's categories, when a better definition would be open and women's. That is, those who are women are in the restricted category, and the rest are in the open group. This would not however solve the Semenya issue, as she identifies as a woman and meets the testosterone criterion. It would be unfair to her to make her run against men. Yet it is also arguably unfair to other women to compete against her, because she creates a problem by running so fast.

If Semenya were to finish honourably midfield in her races, everyone could pat themselves on the back for their inclusiveness, as they did when Oscar Pistorius was allowed to run in non-Paralympic competition. The problem is when the athlete who escapes simple definitions comes out and beats everyone, which Semenya has repeatedly done. Then the complaint of injustice arises, and understandably so. Women who have missed out on Olympic medals or finals places due of Semenya are within their rights to be disappointed, even if you do not agree with them. They also have given their lives to their sport.

It seems that the AFL is hoping to welcome Hannah Mouncey as her transition progresses and she becomes smaller. Just how much smaller, the league does not say. It just wants to feel a bit better and to welcome Mouncey as one of the pack, not as a dominator. There's a certain common sense in that, but such an instinctive approach is too subjective to stand up to a future in which more and more transitioning footballers will be following Mouncey.

Many have an opinion on the Mouncey case, but few offer a solution beyond the IOC's definition, which attempts to offer clarity but is itself arbitrary and a work in progress. Why five years? Why testosterone levels of 10 nanomoles per litre? Fixing a number gives a certain kind of clarity but, like a scoreboard, does not necessarily reflect justice.

I can't condemn the AFL for applying subjective judgment to the Mouncey case. Everybody wants a simple definition and greater transparency, but isn't the demand for simplicity the obstacle in the first place? Sport exists on a foundation of binaries: win/lose, legal/illegal, in/out, man/woman. Yet binaries too often impede fairness. I have great sympathy with Mouncey, even more after her dignified acceptance of the ruling. My gut says she should have been allowed to play. But I understand that the AFL has been forced to choose one item from a menu comprising only different types of unfairness, and the people there know that they have much work to do in the coming years to get this right. But, like their current premiers, they're going to have to fail their way to success.

Yes, this has been a carefully-constructed fence I sit on, but I refuse to get off it. Either side is a plunge into right/wrong, yes/no and good/bad, and as sport is being forced to discover, that simplicity belongs to the past. Fairness to all parties may eventually be found, but it's going to be mistake by mistake until sporting bodies get there. There's no backing away from it, though, because Hannah Mouncey is only the first. We all live in a world in transition.