Sailor upset royal court … (3)
I believe the answer is:
bar
'court' is the definition.
(thesaurus)
'sailor upset royal' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'upset' says the letters should be written in reverse.
'royal' becomes 'r' (abbreviation).
'ab' written backwards gives 'ba'.
'ba'+'r'='BAR'
(Other definitions for bar that I've seen before include "Except - lawyers" , "saving" , "In Mississippi, measure" , "Exclude; sandbank" , "Establishment for the serving of alcoholic drinks" .)