Recover cannabis before gangs finally start fighting (4,2,5)
I believe the answer is:
come to blows
'start fighting' is the definition.
(I've seen this before)
'recover cannabis before gangs finally' is the wordplay.
'recover' becomes 'cometo' (I've seen this before).
'cannabis' becomes 'blow' (I've seen this before).
'before' means one lot of letters go next to another.
'finally' suggests the final letters.
The final letter of 'gangs' is 's'.
'cometo'+'blow'+'s'='COME TO BLOWS'
(Other definitions for come to blows that I've seen before include "Start fighting" , "begin a succession of hits?" , "Result in a fight" .)