- Clans play challenges against other clans. They may also play in the clan leagues, i.e. playing as a team against other teams. Clubs don't play against other clubs.
- Clans are only for subscribers, clubs are open for both subscribers and non-subscribers.
- Clans can have up to 20 members; for clubs, there is no limit so far (I think).
- You can only join up to four clans, but as many clubs as you like.
- Clans can start a private forum with as few as four members; clubs need 20 members to start a private forum.
- Members of clubs with 50 or more members get a club rating in addition to their normal RHP rating. The club rating is only affected by games against members of the same club. Clans don't have their own rating.
I probably forgot some differences.