if organizers judge that having been AMAB is a physical advantage for that sport.
Good idea in theory, pretty unfair in practice. Think about the "physical advantages" that we already accept in elite sports - Michael Phelps, for instance, obviously is an impressive athlete but also has some obvious genetic physical advantages. Think of the shortest man you know and the tallest man you know - are they automatically on an even playing field in basketball because they're both men? Don't we kind of just look past that kind of physical advantage?
My experience in fencing/HEMA is that height is the greatest physical advantage, far beyond AGAB. It's a pretty obvious advantage - more height generally means more reach which means you can hit an opponent before they can hit you. So practice tends to be co-ed, if people are paired off to make equal matches there's a tendency toward equal-height matchups. Then, when we go to compete, there's gender divisions for very little practical reason.
The ultimate issue is that AGAB alone is not a great indicator of athletic performance. "Physical advantages" exist even among cis athletes and trans athletes really only call attention to a problem that exists in elite sports anyway. It's also worth saying that sports science isn't a solved field and we're just now coming around to a better understanding of fascia and just how important it is to movement. Fascia is extremely responsive to hormonal changes and with time will more closely reflect a trans person's hormonal composition than their AGAB.
These sorts of advantages maybe matter in elite competitions, and I am willing to accept that AGAB isn't meaningless when discussing physical advantages, but at an amateur level (where the vast majority of athletes are at) it's a lot less relevant. But unfortunately, our amateur sports mimic elite sports and if elite sports buy into the idea that trans people are just inherently physically different to the extent that they cannot compete in the same way, alongside others' genetic physical advantages, then amateur sports take that attitude too and suddenly you get people pushing for genital inspections in kids' sports.
Yeah, amateur sports mimicking elite sports is a big part of this issue and a microcosm of another issue with exercise culture at large. We're more sedentary than ever, but when we go to the gym or train for a sport, we mimic what elite athletes do, which isn't very appropriate for beginners. An example might be doing a lot of strength building in isolation without bringing it together into broader multi-joint movements, which results in poor motor control.
but anyway I digress. This really all should just be a hell of a lot less serious for the vast majority of us and gendered divisions in amateur sports is another arm of that problem imo.