Less Wrong is as a community extremely nerdy. That's true for almost any definition of "nerd" that captures anyone's intuition for the word. However, to a large extent, many aspects of nerdiness are not connected to rationality at all, even though nerdiness may be associated with more rationality in some limited aspects. For example, fantasy literature is probably not in any deep way connected to either intelligent or rational thinking except for historical reasons.
Yet LW is full of references to science fiction, fantasy literature, anime and D&D. In one recent example, a post started with an only marginally connected tidbit from Heinlein. Moreover, substantial subthreads have arisen bashing aspects of other subcultures. For example, see this subthread where multiple users discuss how spectator sports are "banal" and "pointless". I suspect that this attitude may be turning away not only non-nerds but even the somewhat nerdy who enjoy watching sports, and see it has harmless tribalist fun, not very different than friends arguing over whether Star Wars or Star Trek is superior which has about the same degree of actual value here.
There's a related issue which is a serious point about rationality and human cognition: Our hobbies are to a large extent functions of our specific upbringings and surrounding culture. That some people prefer one form of fantastic escapism involving imaginary spaceships isn't at some level very different than the escapism of watching some people throw and catch objects. Looking down on other people because of these sorts of preferences is unhelpful tribalism. It might feel good, and it might be fun, but it isn't helpful.
If you define nerdiness by the subject matter, then sci fi is nerdy and sports are not. But if you define nerdiness by the approach that people take, then there are plenty of sports nerds (think Bill James, Nate Silver, Moneyball, or this Onion article). Sabermetrics is basically the rationalist approach to sports: figure out what actually helps teams win by collecting the right data, analyzing it appropriately, and following the numbers even if they disagree with established views. This approach is growing rapidly, and has spread to other sports besides baseball (including NBA basketball and NFL football).
Sports could be a gateway drug to a broader interest in rationality, just like scifi/fantasy have been for many people. Maybe we need the sports equivalent of HPMOR?
I once attended an annual convention of classic-appliances afficionados, to keep my husband company, and remember being somewhat disoriented by being surrounded by a community of nerds with whom I simply did not resonate in the slightest, while at the same time clearly recognizing what they were doing as what nerds do when we congregate. It has been a useful memory to keep in mind when watching people be alienated by my own community... affinity is more contingent/superficial than I would necessarily prefer.