Gunners having first approached, react fearfully — not wanting to get shot (6-3)
I believe the answer is:
camera-shy
'react fearfully not wanting to get shot' is the definition.
I can't tell whether this definition defines the answer.
'gunners having first approached' is the wordplay.
'gunners' becomes 'RA' (Royal Artillery).
'having' becomes 'shy' (I can't justify this - if you can you should believe this answer much more).
'first' says to put letters next to each other.
'approached' becomes 'came' (come can mean to approach or get closer).
'ra'+'shy'='rashy'
'rashy' put after 'came' is 'CAMERA-SHY'.
Can you help me to learn more?
(Other definitions for camera-shy that I've seen before include "Afraid of the lens" , "Chaser may be apprehensive of having photo taken - bashful?" , "Reluctant to be photographed" , "Unwilling to be photographed" .)