Conservative with flair upset opposing side (6)
I believe the answer is:
contra
'opposing side' is the definition.
(prefix meaning on the opposite side)
'conservative with flair upset' is the wordplay.
'conservative' becomes 'con' (abbreviation for Conservative).
'with' says to put letters next to each other.
'flair' becomes 'art' (flair can mean artiness or creativity).
'upset' shows that the letters should be reversed in order.
'art' back-to-front is 'tra'.
'con'+'tra'='CONTRA'
(Other definitions for contra that I've seen before include "Against in argument" , "Revolutionary fighter" , "guerrilla" , "(One) opposed (to the Sandinistas)" , "Rebel fighter" .)