Where shooting happens, for a start (5)
I believe the answer is:
onset
This clue might be a double definition.
'where shooting happens' is the first definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'a start' is the second definition.
(onset is a kind of start)
'for' acts as a link.
Can you help me to learn more?
(Other definitions for onset that I've seen before include "Appearance of" , "17 down [ASSAULT]" , "Advent" , "Start - notes (anag)" , "Stone (anag)" .)