On r/nba, I've seen several posts looking at basketball forums from as far back as 1986. However, in my own research about the internet (I did a small project on how it was invented in high school), I read that it was originally only available to academic researchers, and used as a means to advance research. When did online communities like anime or sports forums start forming, and what were the factors that drove this formation?
Usenet news started in 1980 and was split up into news.groups for different topics. These were named news.<topic>.
In 1986, the Great Renaming happened and multiple top level hierarchies were created. Sci, comp, misc, alt, talk and so on.
Although it could use the Internet as a transport, Usenet did not require an Internet connection. UUCP would also work over multiple dial up modem connections.
For instance, the first News site I ever set up had a dial up connection to a site called 'yenta' . We'd exchange news articles every 15 min with them. Yenta, in turn, had a dial up connection to bbx. My recollection is that bbx was actually on the Internet, but this was 25 years ago, so my memory on that could be faulty.
As an aside, this same mechanism is how we sent/received email.
My recollection is that CompuServ had discussion groups earlier than that, but I don't know much about those.