Prisoner's name sewn into socks (7)
I believe the answer is:
hostage
'prisoner's' is the definition.
(hostage is a kind of prisoner)
'name sewn into socks' is the wordplay.
'name' becomes 'tag' (I've seen this in other clues).
'sewn into' means one lot of letters goes inside another.
'socks' becomes 'hose' (I've seen this in other clues).
'tag' placed inside 'hose' is 'HOSTAGE'.
(Other definitions for hostage that I've seen before include "Kidnap victim" , "Person held by kidnapper for ransom" , "Prisoner held as security" , "One seized as security" , "Prisoner - pawn" .)