Saint imprisoned by king, say, one taking stock (7)
I believe the answer is:
rustler
'one taking stock' is the definition.
(someone stealing farm animals ie stock)
'saint imprisoned by king' is the wordplay.
'saint' becomes 'st' (abbreviation).
'imprisoned by' indicates putting letters inside.
'king' becomes 'ruler' (I've seen this before).
'st' inserted inside 'ruler' is 'RUSTLER'.
'say' is the link.
(Other definitions for rustler that I've seen before include "Horse thief" , "Cattle-thief" , "lawbreaker" , "One who takes livestock" , "one whose stock-taking is dishonest" .)