Tar assigned to rear of deck produces instrument (9)
I believe the answer is:
pitchfork
'instrument' is the definition.
(thesaurus)
'tar assigned to rear of deck' is the wordplay.
'tar' becomes 'pitch' (synonyms).
'assigned' is a charade indicator (letters next to each other).
'to' becomes 'for'.
'rear of' indicates one should take the final letters.
The final letter of 'deck' is 'k'.
'pitch'+'for'+'k'='PITCHFORK'
'produces' acts as a link.
(Other definitions for pitchfork that I've seen before include "Tool for lifting hay" , "Tool for shifting hay" , "multi-pronged tool" , "Tool for tossing hay" , "Thrust into a difficult situation" .)