Leave concerning bloodshed (4)
I believe the answer is:
gore
'bloodshed' is the definition.
(I know that bloodshed can be written as gore)
'leave concerning' is the wordplay.
'leave' becomes 'go' (to go is to depart or leave).
'concerning' becomes 're' (both can mean on a particular topic).
'go'+'re'='GORE'
(Other definitions for gore that I've seen before include "Blood that's been shed" , "Bloodshed" , "Make a hole in" , "piece of material" , "Impale" .)