Supporter trouble is on the rise for City (8)
I believe the answer is:
brasilia
'city' is the definition.
(capital of Brazil)
'supporter trouble is on the rise' is the wordplay.
'supporter' becomes 'bra' (a bra gives support to breasts).
'trouble' becomes 'ail' (synonyms).
'on the rise' is a reversal indicator (in a down clue, letters go up).
'ail'+'is'='ailis'
'ailis' in reverse letter order is 'silia'.
'bra'+'silia'='BRASILIA'
'for' is the link.
(Other definitions for brasilia that I've seen before include "South American capital" , "Capital city of Brazil" , "11 [CAPITAL]" , "SA capital" .)