A few hours after World Athletics announced it had banned transgender women from elite female sport, someone tagged Parkrun UK in a tweet, and asked: “Will you follow @WorldAthletics lead and ban transgender women from women’s athletics at all levels?” It was only one post by one person with a hundred-odd followers, but the tweet calling for transgender women to be barred from an organised run was seen by nearly 20,000 people in 24 hours.

In purely sporting terms, the transgender debate is about long-standing dividing lines built on the biological differences between men and women, which are being tested by the reality that not everyone fits neatly into those boxes. It is about biology and identity, about sex and gender, about finding an impossible balance between the principle of fairness and the right of inclusion. But when a major sporting body makes a decision on transgender exclusion like this one, there will inevitably be unintended consequences at every level.

The detailed 2021 Trans Lives Survey found 77 per cent of trans women who participate in sport have experienced transphobia, and 14 per cent experience abuse or discrimination “every time” they play. As Australian trans-runner Ricki Coughlan warned this week, World Athletics’ decision could now embolden “forces of hate” against the community, because the notion of exclusion will permeate far deeper than elite sport.

The odd part is that athletics’ new regulations are not particularly consequential within the sport itself. Trans athletes are not toppling world records or sweeping up gold medals. As the transitioned Canadian cyclist Kristen Worley pointed out: “I’m watching all the news groups put out images on Twitter with no images of transitioned athletes at the elite levels of the World Athletics, because there aren’t any.” From a sporting perspective, the most relevant part of Thursday’s announcement concerned athletes with DSD (differences in sexual development) like Caster Semenya and Christine Mboma, both of whom are Olympic medallists with some male biological characteristics.

They have effectively been banned from the World Athletics Championships later this year, and must adhere to new stricter rules on suppressing testosterone levels if they are ever to return. Y e t W o r l d Athletics t o o k a n even stronger stance against the potential rise of trans-women athletes. It cited evidence of the long-term benefits of male puberty on physical attributes like strength and endurance, benefits which cannot fully be undone by hormonal therapy treatment, and concluded that nontransgender women would be at a disadvantage in competition. The president of World Athletics, Sebastian Coe, insisted the decision was “guided by the science around physical performance”. The ruling does at least bring some clarity to a clouded part of the sport. Coe promised an ongoing review of the regulations as new science emerges and announced a “Working Group for 12 months to further consider the issue”.

But only one trans athlete will be included on the dozen-strong committee, and it seems unlikely that any significant new evidence will come to light. “For the past 12 years World Athletics have been allowing transgender women to compete in international competition if they lower testosterone,” the Loughborough University researcher and athlete Joanna Harper told BBC Radio 5 Live. “However, not a single transgender woman has qualified for international-level athletics. Trans women were not on the verge of taking over … If World Athletics is really interested in getting more data, banning trans women from international athletics is not the way to get it.” Some athletes have welcomed the news, like British Olympic runner Emily Diamond who celebrated “a big step for fairness and protecting the female category”. The campaign group Fair Play For Women called for British Athletics to follow World Athletics’ lead, saying: “We now expect to see national federations restore the talent pathway for girls and young women, and to reinstate fair sport for women of all ages.”

Almost every side of the argument is right, in some way, which is why it is so complex and so nuanced. Transgender women do have an athletic advantage over non-transgender women, and the very point of a women’s category is to create a biological level-playing field away from male advantage. But transgender exclusion is now implicit in the foundations of athletics, and that premise will be felt in sports clubs and communities all around. World Athletics has made a sporting decision, one that it believes upholds the integrity and fairness of competition.

But the wider consequences are unquantifiable and almost certainly detrimental to an already marginalised class without a voice. So perhaps the most concerning part is not the effect on the sport itself, but that on the day a major governing body delivered an elite-level ruling, someone somewhere called for transgender women to be banned from running around their local park.