Poet is writer held by revolutionary communists (7)
I believe the answer is:
spender
'poet' is the definition.
(Stephen Spender)
'writer held by revolutionary communists' is the wordplay.
'writer' becomes 'pen' (I've seen this before).
'held by' is an insertion indicator.
'revolutionary' says the letters should be written backwards.
'communists' becomes 'reds' (red is a kind of communist).
'reds' reversed gives 'sder'.
'pen' placed inside 'sder' is 'SPENDER'.
'is' is the link.
(Other definitions for spender that I've seen before include "who is just 31[WINDOW SHOPPER]? No" , "writer of poetry" , "One paying out money" , "One using money" , "Profligate" .)