Threatening much initially in a Test, but bagging duck (8)
I believe the answer is:
minatory
'threatening' is the definition.
(formal term meaning threatening)
'much initially in a test but bagging duck' is the wordplay.
'initially' suggests taking the first letters.
'test' becomes 'try' (synonyms).
'but bagging' is an insertion indicator.
'duck' becomes 'o' (resembles zero - 'duck' in cricket).
The first letter of 'much' is 'm'.
'try' going around 'o' is 'tory'.
'm'+'in'+'a'+'tory'='MINATORY'
(Other definitions for minatory that I've seen before include "Threatening tragic developments - try Naomi (anag)" , "Threatening, indicative of wish to harm" , "Menacing" , "Into army (anag.)" .)