No longer confined, holding on for advocate? (8)
I believe the answer is:
exponent
'advocate?' is the definition.
(I've seen this before)
'no longer confined holding on' is the wordplay.
'no longer' becomes 'ex'.
'confined' becomes 'pent' ('pent' can be similar in meaning to 'confined').
'holding' is an insertion indicator.
'pent' going around 'on' is 'ponent'.
'ex'+'ponent'='EXPONENT'
'for' acts as a link.
(Other definitions for exponent that I've seen before include "Skilled performer" , "skilful practitioner" , "Promoter (of an idea or theory)" , "Interpreter - performer" , "Symbol of power" .)