Great enthusiasm, or sudden blow linked to duck? (5)
I believe the answer is:
gusto
'great enthusiasm' is the definition.
(I've seen this in another clue)
'sudden blow linked to duck?' is the wordplay.
'sudden blow' becomes 'gust' (I've seen this in another clue).
'linked to' is a charade indicator (letters next to each other).
'duck?' becomes 'o' (resembles zero - 'duck' in cricket).
'gust'+'o'='GUSTO'
'or' is the link.
(Other definitions for gusto that I've seen before include "exhilaration" , "(Corporate) emblem" , "Zest, pleasure in action" , "Hearty enjoyment" , "Vigorous enthusiasm" .)