Small-minded sort of officer? (5)
I believe the answer is:
I believe this clue is a double definition.
'small-minded' is the first definition.
'sort of officer?' is the second definition.
(Other definitions for petty that I've seen before include "Trivial, contemptible" , "Insignificant or trivial" , "This cash is of a trivial amount" , "Trivial, piffling" , "small" .)