One football team? (6)
I believe the answer is:
united
I believe this is a double definition.
'one' is the first definition.
(synonyms)
'football team' is the second definition.
(eg Manchester United)
(Other definitions for united that I've seen before include "in league" , "See 9" , "See 14" , "Joined together -- in duet (anag)" , "cooperative" .)