Notice trim rations upset manager (13)
I believe the answer is:
administrator
'manager' is the definition.
(I've seen this before)
'notice trim rations upset' is the wordplay.
'notice' becomes 'ad' (both can mean an advertisement).
'upset' is an anagram indicator.
'trim'+'rations'='trimrations'
'trimrations' with letters rearranged gives 'ministrator'.
'ad'+'ministrator'='ADMINISTRATOR'
(Other definitions for administrator that I've seen before include "Runner" , "Business organiser" , "Official organiser" , "One who manages or directs" , "Executive" .)