Criticise American revolutionary's swagger (7)
I believe the answer is:
panache
'swagger' is the definition.
(thesaurus)
'criticise american revolutionary's' is the wordplay.
'criticise' becomes 'pan' (informal term meaning to criticise heavily).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'revolutionary' becomes 'che' (Che Guevara the Marxist revolutionary).
'pan'+'a'+'che'='PANACHE'
(Other definitions for panache that I've seen before include "Grand manner, theatricality" , "Style, elan" , "'Dash, flair (7)'" , "A confident stylish manner" , "Flamboyant confidence" .)