Spot a misplaced bolt (4)
I believe the answer is:
blot
'spot' is the definition.
('blot' can be a synonym of 'spot')
'a misplaced bolt' is the wordplay.
'a misplaced' is an anagram indicator.
'bolt' anagrammed gives 'BLOT'.
(Other definitions for blot that I've seen before include "stain on reputation" , "Smudge (on escutcheon?)" , "Soak up (ink); blemish" , "Smudge of ink" , "Stain left by spilled ink" .)