It hurts when father is at home (4)
I believe the answer is:
pain
'it hurts' is the definition.
(I've seen this in another clue)
'father is at home' is the wordplay.
'father' becomes 'pa' (pa can mean dad or father).
'is at home' becomes 'in' ('I'm in' can mean 'I'm at home').
'pa'+'in'='PAIN'
'when' acts as a link.
(Other definitions for pain that I've seen before include "Annoying person" , "French bread?" , "Physical hurt" , "Hurt feeling" , "Mental distress" .)