A battalion rebel over scene of bloodshed (8)
I believe the answer is:
abattoir
'scene of bloodshed' is the definition.
(where animals are slaughtered)
'a battalion rebel over' is the wordplay.
'battalion' becomes 'bat' (abbreviation).
'rebel' becomes 'riot' (both can mean to cause a disturbance).
'over' says the letters should be written backwards.
'riot' backwards is 'toir'.
'a'+'bat'+'toir'='ABATTOIR'
(Other definitions for abattoir that I've seen before include "it makes a killing" , "[EASY MEAT] half-cut seen here?" , "Make smile for camera" , "scene of slaughter" , "Damage (metal) by chemical action" .)