Unsubtle alternative to the key ingredient in fried fish, in metric weight (9,3)
I believe the answer is:
battering ram
'unsubtle alternative to the key' is the definition.
(a battering ram might smash through a door lock)
'ingredient in fried fish in metric weight' is the wordplay.
'ingredient in fried fish' becomes 'batter' (fish is fried in batter).
'metric weight' becomes 'gram' (I've seen this before).
'batter'+'in'+'gram'='BATTERING-RAM'
(Other definitions for battering ram that I've seen before include "Large beam with which to knock down walls" , "Siege weapon" , "ensures successful entre?" , "Door-forcing pole" , "Means of breaking down walls etc" .)