Onslaught from ethnic group on withdrawal of charity (8)
I believe the answer is:
diatribe
'onslaught' is the definition.
(I have seen 'Verbal onslaught' mean 'diatribe' so perhaps 'onslaught' could also mean 'diatribe')
'ethnic group on withdrawal of charity' is the wordplay.
'ethnic group' becomes 'tribe' (I've seen this in another clue).
'on' is a charade indicator (letters next to each other).
'withdrawal of' shows that the letters should be reversed in order.
'charity' becomes 'aid' (eg foreign aid).
'aid' reversed gives 'dia'.
'tribe' put after 'dia' is 'DIATRIBE'.
'from' acts as a link.
(Other definitions for diatribe that I've seen before include "critical speech" , "Bitter words" , "A Prolonged harangue" , "Abusive harangue" , "'Abusive, bitter speech (8)'" .)