Mockery, flag supporting it (6)
I believe the answer is:
satire
'mockery' is the definition.
(thesaurus)
'flag supporting it' is the wordplay.
'flag' becomes 'tire' (I've seen this before).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'it' becomes 'sa' (old-fashioned abbreviation for sex appeal).
'tire' after 'sa' is 'SATIRE'.
(Other definitions for satire that I've seen before include "Irony or sarcasm in speech or writing" , "Pointed humour" , "Writings ridiculing vice and folly" , "Humerous literary ridicule" , "Jonathan Swift's forte?" .)