Sudden blow besetting European visitor (5)
I believe the answer is:
guest
'visitor' is the definition.
(someone visiting a place)
'sudden blow besetting european' is the wordplay.
'sudden blow' becomes 'gust' (I've seen this before).
'besetting' means one lot of letters goes inside another.
'european' becomes 'E' (abbreviation e.g. EU).
'gust' going around 'e' is 'GUEST'.
(Other definitions for guest that I've seen before include "Visitor to whom hospitality is extended" , "Recipient of hospitality" , "who takes hotel room" , "Visitant" , "Conjectured audibly" .)