Prisoners not out with friends (7)
I believe the answer is:
inmates
'prisoners' is the definition.
(inmate is a kind of prisoner)
'not out with friends' is the wordplay.
'not out' becomes 'in' ('in' is the opposite to 'out').
'with' is a charade indicator (letters next to each other).
'friends' becomes 'mates' (mate is a kind of friend).
'in'+'mates'='INMATES'
(Other definitions for inmates that I've seen before include "Inhabitants" , "Ties man (anag.)" , "Prisoners" .)