Criticise a revolutionary's swagger (7)
I believe the answer is:
panache
'swagger' is the definition.
(I've seen this before)
'criticise a revolutionary's' is the wordplay.
'criticise' becomes 'pan' (informal term meaning to criticise heavily).
'revolutionary' becomes 'Che' (Che Guevara the Marxist revolutionary).
'pan'+'a'+'che'='PANACHE'
(Other definitions for panache that I've seen before include "A confident stylish manner" , "Flamboyant confidence" , "stylish carriage" , "Flamboyance - style" , "'Dash, flair (7)'" .)