Ordinary seaman can in the course of fund-raising event (6)
I believe the answer is:
rating
'ordinary seaman' is the definition.
(I've seen this before)
'can in the course of fund-raising event' is the wordplay.
'can' becomes 'tin' (synonyms).
'in the course of' is an insertion indicator.
'fund-raising event' becomes 'rag' (university charity event).
'tin' put within 'rag' is 'RATING'.
(Other definitions for rating that I've seen before include "How many watched TV" , "Salt" , "Classification; seaman" , "Angry reprimand for non-commissioned sailor?" , "Score" .)