Old weapon broken by the new weapon (7)
I believe the answer is:
machete
'weapon' is the definition.
(machete is a kind of weapon)
'old weapon broken by the new' is the wordplay.
'old weapon' becomes 'mace' (I've seen this in another clue).
'broken by' is an insertion indicator (inserted letters break into the word).
'new' indicates anagramming the letters.
'the' anagrammed gives 'het'.
'mace' enclosing 'het' is 'MACHETE'.
(Other definitions for machete that I've seen before include "Broad heavy knife common in Central America" , "Teach me with large jungle knife" , "Broad heavy knife used in S American jungles" , "hacker" , "Cheat me over broad heavy knife used in jungle" .)