From Halopedia, the Halo wiki
A Clanmatch is a Halo 2 multiplayer option. It consists of ranked matches between clans that can have up to 10 people participating. Determines clan rank instead of personal rank.
Min Players: 8
Max Players: 10
Team Count: 2 (one per clan)
Min Party Size: 4
Max Party Size: 5
Special restrictions: must all be in the same clan
Uses Team Slayer and Team Skirmish Playlists.