Petty sergeant major everybody disliked (5-6)
I believe the answer is:
small-minded
'petty' is the definition.
(I know that petty can be written as small-minded)
'sergeant major everybody disliked' is the wordplay.
'sergeant major' becomes 'SM' (abbreviation for sergeant major).
'everybody' becomes 'all' (I've seen this before).
'disliked' becomes 'minded' (to mind something is to dislike or object to it).
'sm'+'all'+'minded'='SMALL-MINDED'
(Other definitions for small-minded that I've seen before include "Petty" , "Intolerant" .)