Draft piece of writing by prisoner (9)
I believe the answer is:
conscript
'draft piece' is the definition.
'conscript' can be an answer for 'draft' (conscripting is a kind of drafting). I'm unsure of the 'piece' bit.
'writing by prisoner' is the wordplay.
'writing' becomes 'script' (script is a kind of writing).
'by' means one lot of letters go next to another.
'prisoner' becomes 'con' (abbreviation for 'convict').
'script' put after 'con' is 'CONSCRIPT'.
'of' is the link.
Can you help me to learn more?
(Other definitions for conscript that I've seen before include "Compulsorily enlisted person" , "One enrolled" , "draft on Broadway?" , "Enlist compulsorily" , "Draftee" .)