Sailor called about trip without regulars (6)
I believe the answer is:
rating
'sailor' is the definition.
(British term for a naval enlisted man)
'called about trip without regulars' is the wordplay.
'called' becomes 'rang' ('ring' can be a synonym of 'call').
'about' means one lot of letters goes inside another.
'without regulars' means one should take alternating letters (letters must be removed at regular intervals).
The alternating letters of 'trip' are 'ti'.
'rang' enclosing 'ti' is 'RATING'.
(Other definitions for rating that I've seen before include "Salt" , "Doing an appraisal" , "Grading or ranking" , "level" , "Score" .)