The BB Community is frequently cited as one of the strongest elements of the game. You can find fellow coaches on multiple platforms on the web.
Below are samples of the groups on Facebook to discuss the game. Several national communities can be found there as well if you search for them.
A Reddit community with more than 30,000 members dwells at r/bloodbowl.
Forums
While a lot of discussions have transitioned to the large social networks, there are still many active BB forums, from global to national ones.
TFF is the granddad of Blood Bowl forums, and contains a lot of tournament discussion, particularly for the UK scene. You can also find out about other Fantasy Football games.
FUMBBL has an extremely active forum and Discord server for discussion of tactics and strategy applicable to tabletop play as well as the leagues and tournaments on FUMBBL.
The Members Area includes a forum to discuss tournaments, tactics, miniatures and more. However, these discussion have moved largely to the NAF Discord server.
There are then forums to discuss Blood Bowl in various languages or on a national level: