Mum on run hurt (3)
I believe the answer is:
mar
'hurt' is the definition.
(I know that mar is a type of maim)
'mum on run' is the wordplay.
'mum' becomes 'ma' (ma can mean mother).
'on' is a charade indicator (letters next to each other).
'run' becomes 'r' (cricket abbreviation).
'ma'+'r'='MAR'
(Other definitions for mar that I've seen before include "Blight" , "Spoil or deface" , "Ram into and spoil" , "Spoil stuff" , "Detract from" .)