Support backing people in fierce speech (8)
I believe the answer is:
diatribe
'fierce speech' is the definition.
(a diatribe is an angry speech)
'support backing people' is the wordplay.
'support' becomes 'aid' (to aid is to help or support).
'backing' is a reversal indicator.
'people' becomes 'tribe' (I've seen this in other clues).
'aid' in reverse letter order is 'dia'.
'dia'+'tribe'='DIATRIBE'
'in' acts as a link.
(Other definitions for diatribe that I've seen before include "Vitriolic speech" , "Bitter verbal attack" , "Abusive harangue" , "Strong words" , "stream of abuse" .)