Label put into socks for prisoner (7)
I believe the answer is:
hostage
'for prisoner' is the definition.
(someone taken as a prisoner)
'label put into socks' is the wordplay.
'label' becomes 'tag' (synonyms).
'put into' is an insertion indicator.
'socks' becomes 'hose' (I've seen this in other clues).
'tag' placed into 'hose' is 'HOSTAGE'.
(Other definitions for hostage that I've seen before include "One caught" , "Person held by kidnappers" , "Prisoner held as security" , "Detainee - gash toe (anag)" , "person captive to fortune" .)