Given a part to play, dad shows promise (6)
I believe the answer is:
parole
'promise' is the definition.
(I know that parole is a type of promise)
'given a part to play dad' is the wordplay.
'given' is a charade indicator (letters next to each other).
'a part to play' becomes 'role' (I've seen this before).
'dad' becomes 'pa' (both can mean one's father).
'role' after 'pa' is 'PAROLE'.
'shows' is the link.
(Other definitions for parole that I've seen before include "Temporary release on promise of good behaviour" , "Promise of not escaping etc" , "Promise - conditional release" , "Early release on promise of good behaviour" , "Release of prisoner promising good behaviour" .)