Exist as teams, furthermore (7)
I believe the answer is:
besides
'furthermore' is the definition.
(synonyms)
'exist as teams' is the wordplay.
'exist as' becomes 'be'.
'teams' becomes 'sides' (eg football sides).
'be'+'sides'='BESIDES'
(Other definitions for besides that I've seen before include "Additionally" , "Moreover" , "also is available" , "to boot" , "What's more" .)