Pity about TV detective (7)
I believe the answer is:
remorse
'pity' is the definition.
(I've seen this before)
'about tv detective' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'tv detective' becomes 'Morse' (Inspector Morse).
're'+'morse'='REMORSE'
(Other definitions for remorse that I've seen before include "Gnawing pain of conscience" , "Compunction" , "Ruefulness" , "Guilty conscience" , "Distress from a sense of guilt" .)