Big blow to our sailors before a party (7)
I believe the answer is:
tornado
'big blow' is the definition.
(I've seen this in another clue)
'to our sailors before a party' is the wordplay.
'our sailors' becomes 'RN' (Royal Navy).
'before' is a charade indicator (letters next to each other).
'party' becomes 'do' (do can informally mean a party).
'to'+'rn'+'a'+'do'='TORNADO'
(Other definitions for tornado that I've seen before include "Destructive wind vortex" , "Donator of fierce wind" , "Terrible storm" , "Whirling windstorm" , "great deal of wind" .)