Unit repel charge by half-destroyed sector (6)
I believe the answer is:
parsec
'unit' is the definition.
(I have seen 'astronomical unit' mean 'parsec' so perhaps 'unit' could also mean 'parsec')
'repel charge by half-destroyed sector' is the wordplay.
'repel' says the letters should be written backwards (I've seen 'repelled' mean this).
'charge' becomes 'rap' (both can mean blame or responsibility).
'by' says to put letters next to each other.
'half destroyed' suggests halving the letters.
'rap' written backwards gives 'par'.
'sector' cut in half is 'sec'.
'par'+'sec'='PARSEC'
(Other definitions for parsec that I've seen before include "Unit of distance in astronomy" , "fair distance" , "far in the distance" , "Long way" , "Three+ light-years" .)