Smart, supporter at home -- and away, ultimately (6)
I believe the answer is:
brainy
'smart' is the definition.
(thesaurus)
'supporter at home and away ultimately' is the wordplay.
'supporter' becomes 'bra' (I've seen this before).
'at home' becomes 'in' ('in' can be similar in meaning to 'at home').
'and' is a charade indicator (letters next to each other).
'ultimately' suggests the final letters.
The final letter of 'away' is 'y'.
'bra'+'in'+'y'='BRAINY'
(Other definitions for brainy that I've seen before include "Having a high IQ" , "Bright" , "Intellectual" , "Intelligent, clever." , "Highly intelligent" .)