Sailor upsetting a rascal (6)
I believe the answer is:
lascar
'sailor' is the definition.
(I know that Lascar is a type of sailor)
'upsetting a rascal' is the wordplay.
'upsetting' indicates an anagram.
'rascal' is an anagram of 'LASCAR'.
(Other definitions for lascar that I've seen before include "Camp-follower" , "E. Indian seaman" , "Asian sailor" , "Kind of foreign sailor - quite a rascal" , "Rascal (anag) - oriental seaman" .)