Senior officers stop bars becoming disorderly (3,5)
I believe the answer is:
top brass
'senior officers' is the definition.
(I've seen this before)
'stop bars becoming disorderly' is the wordplay.
'becoming disorderly' indicates anagramming the letters (I've seen this in other clues).
'stop'+'bars'='stopbars'
'stopbars' is an anagram of 'TOP-BRASS'.
(Other definitions for top brass that I've seen before include "Most important leaders, officers, etc" , "Leadership" , "Important people" , "senior command" , "military leaders" .)