Gunnery from angry sack (9)
I believe the answer is:
crossfire
'gunnery from angry sack' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'angry sack' is the wordplay.
'angry' becomes 'cross' (cross can mean annoyed or angry).
'sack' becomes 'fire' (synonyms).
'cross'+'fire'='CROSSFIRE'
Can you help me to learn more?
(Other definitions for crossfire that I've seen before include "argument" , "fierce exchange" , "lively exchange of opinions" , "Hail of bullets" , "bullets coming from all sides" .)