It's pitiful when father gets the twitch (8)
I believe the answer is:
pathetic
'it's pitiful' is the definition.
(synonyms)
'father gets the twitch' is the wordplay.
'father' becomes 'pa' (pa can mean dad or father).
'gets' says to put letters next to each other.
'twitch' becomes 'tic' (tic is a kind of twitch).
'pa'+'the'+'tic'='PATHETIC'
'when' acts as a link.
(Other definitions for pathetic that I've seen before include "Arousing pity or sadness" , "Feeble; inspiring pity" , "Sad - hopeless" , "Tip cheat - truly sad" , "Pitiable, inadequate" .)