Sketch doctor at the back (5)
I believe the answer is:
draft
'sketch' is the definition.
(draft is a kind of sketch)
'doctor at the back' is the wordplay.
'doctor' becomes 'Dr' (abbreviation).
'at' is a charade indicator (letters next to each other).
'the back' becomes 'aft' (I've seen this in other clues).
'dr'+'aft'='DRAFT'
(Other definitions for draft that I've seen before include "plan outlined" , "Sketch - detachment of men" , "A money order for US conscription" , "Draw an outline" , "Sketch; money order" .)