Boycott a cost rise that's outrageous (9)
I believe the answer is:
ostracise
'boycott' is the definition.
('boycott'->'ostracize' is in my internal thesaurus and 'ize'->'ise')
'a cost rise that's outrageous' is the wordplay.
'that's outrageous' indicates an anagram (I've seen this in other clues).
'a'+'cost'+'rise'='acostrise'
'acostrise' with letters rearranged gives 'OSTRACISE'.
(Other definitions for ostracise that I've seen before include "I, Socrates may exclude from group" , "Socrates and I are made to exclude from society" , "Blackball, send to Coventry" , "Drive out" , "Cast out, send to Coventry" .)