Weapon initially fired in anger (5)
I believe the answer is:
rifle
'weapon' is the definition.
(rifle is a kind of weapon)
'initially fired in anger' is the wordplay.
'initially' suggests taking the first letters.
'in' is an insertion indicator.
'anger' becomes 'rile' (I've seen this before).
The first letter of 'fired' is 'f'.
'f' placed into 'rile' is 'RIFLE'.
(Other definitions for rifle that I've seen before include "Steal and carry off - firearm" , "Search and rob - with long gun?" , "Author of report" , "Ransack; a weapon" , "Shoulder weapon" .)