Pain is no good to father (4)
I believe the answer is:
pang
'pain' is the definition.
(pang is a kind of pain)
'no good to father' is the wordplay.
'no good' becomes 'ng' (abbreviation).
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'father' becomes 'pa' (pa can mean dad or father).
'ng' after 'pa' is 'PANG'.
'is' is the link.
(Other definitions for pang that I've seen before include "Sharp pain (or similar feeling)" , "Stab of pain" , "Sharp twinge of pain" , "Brief painful feeling" , "Sharp spasm of pain" .)