Supporters with lots of hard facts (5,5)
I believe the answer is:
brass tacks
'hard facts' is the definition.
(I've seen this before)
'supporters with lots' is the wordplay.
'supporters' becomes 'bras' (I've seen this in other clues).
'with' is a charade indicator (letters next to each other).
'lots' becomes 'stacks' ('stack' can be a synonym of 'lot'**).
'bras'+'stacks'='BRASS TACKS'
'of' acts as a link.
(Other definitions for brass tacks that I've seen before include "Basic realities (informal)" , "Real business" , "Business one gets down to" , "Hard facts" , "Details of practical business (colloq.)" .)