This thread sheds a new light on the length of some other threads in this forum. The length of this thread should be close to zero but apparently we still find a lot to discuss.
There is a lot of room for debate on the quality of contributions, but surely there's little room for debate that this is an important question for go players. Access to the Olympics at one extreme, or to funding from local councils or schools at another extreme, depends on the answer. If a killer answer could be found, that access could be gained and could transform the fortunes of the game.
It is certainly pointless trying to define a sport. People understand it by what they associate with it. It seems that in English, people nearly always associate it with physical activity, with competition (and so with rules, but not necessarily with an organising body), and with something normally or best done outdoors or in stadiums. Further, the physical activity is not enough per se: it usually has to be an activity where a physical skill decides the result.
But even within that widely shared (and quite small) nexus, there is huge room for disagreement. For example, many people think synchronised swimming is not a true sport: it an activity where rules have been artificially grafted on. But even people who frown on synch swimming will tend to accept ice dancing - perhaps because it is more overtly physical?. But the events on tv around the world that feature celebs and pros dancing against each other in competition apparently share all the common attributes of a sport but no-one thinks of it as sport. The entertainment factor presumably outweighs the sporting factor, and perhaps the factor that it is not open to anyone (and/or is a clearly artificial creation) counts against it.
Is playing football on the playground sport? Many people would regard that as either recreation or physical education. They may agree it is sport if pushed, but don't think of it as sport spontaneously or primarily. Similarly, Tiger Woods' form of golf may be sport, but two old retirees pottering round a golf course to see who buys the next round of drinks has vey different nuances.
Given that kind of inherent confusion, organisations such as the Nihon Ki-in or the China Weiqi Association have tried to exploit the ambiguities in the hope of labelling go as a sport. They have failed, but probably not because of semantics. The more likely reason is that the sports that already have access to the Olympics or funding are usually keen to make sure that no other horses come to drink at their trough. They have found it easy to use the semantics to beat off the incomers, but the real weapon in their armoury was implacable hostility.
So far, the chess and go worlds have licked their wounds and tried t organise a brand new show - mind sports. The fact that most other people easily accept the term shows that they recognise there is some element of sport in both games, so it may be worth someone trying still to come up with a killer argument for the Olympics, but to me it seems more likely that the rise and rise of computers in go will attenuate the already not-strong association of board games with sport in the minds of most outsiders.
What seems to follow from that strategically is that chess and go should pool their resources and build up the image of mind sports as something that can stand proudly beside (physical) sport.
However, while we already have sports jackets, I'm not sure that we'll ever have mind sports jackets (tweedy checks with elbow pads come close but no cigar).