Nudge holding a balance (9)
I believe the answer is:
remainder
'balance' is the definition.
(I've seen this before)
'nudge holding a' is the wordplay.
'nudge' becomes 'reminder' (I've seen this before).
'holding' indicates putting letters inside.
'reminder' placed around 'a' is 'REMAINDER'.
(Other definitions for remainder that I've seen before include "Unsold copy of book" , "Surplus" , "butt" , "deposit" , "Residue" .)