Figure of helper upset over weight (7)
I believe the answer is:
diagram
'figure' is the definition.
(I've seen this in another clue)
'helper upset over weight' is the wordplay.
'helper' becomes 'aid' (something which helps).
'upset over' says the letters should be written backwards (knocked over).
'weight' becomes 'gram' (unit of weight).
'aid' backwards is 'dia'.
'dia'+'gram'='DIAGRAM'
'of' acts as a link.
(Other definitions for diagram that I've seen before include "A grid, Ma? (Anag)" , "Explanatory drawing or plan" , "Explanatory figure" , "Simple schematic" , "Explanatory illustration" .)