Scrapper's initial boost when wrestling (12)
I believe the answer is:
abolitionist
'scrapper's' is the definition.
(someone who wants to scrap or abolish something)
'initial boost when wrestling' is the wordplay.
'when wrestling' indicates anagramming the letters (letters must be wrestled or manoeuvred around).
'initial'+'boost'='initialboost'
'initialboost' is an anagram of 'ABOLITIONIST'.
(Other definitions for abolitionist that I've seen before include "One against, eg, slavery" , "Anti-slavery campaigner" , "One favouring end of capital punishment" , "Reformer (eg Wilberforce)" .)