Scope for mum to get upset a little (5)
I believe the answer is:
ambit
'scope' is the definition.
(synonyms)
'mum to get upset a little' is the wordplay.
'mum' becomes 'ma' (ma can mean mother).
'to get upset' is a reversal indicator (I've seen 'getting upset' mean this).
'a little' becomes 'bit' (both can mean a small amount of something).
'ma' reversed gives 'am'.
'am'+'bit'='AMBIT'
'for' acts as a link.
(Other definitions for ambit that I've seen before include "Scope or circuit" , "Circumference" , "Scope or confines" , "Circuit, compass" , "Compass, scope" .)