St Paul converted with a blunt instrument (7)
I believe the answer is:
spatula
'blunt instrument' is the definition.
'st paul converted with a' is the wordplay.
'converted with' indicates anagramming the letters.
'st'+'paul'='stpaul'
'stpaul' with its letters anagrammed with 'a' can make 'SPATULA'.
(Other definitions for spatula that I've seen before include "flat mixer" , "Implement with broad blunt and often flexible blade" , "Broad implement for mixing or spreading" , "Tool with broad flexible blade - alas, put away" , "Food turner with flexible blade" .)