No thugs mess with this weapon (7)
I believe the answer is:
shotgun
'this weapon' is the definition.
(shotgun is a kind of weapon)
'no thugs mess' is the wordplay.
'mess' indicates an anagram.
'no'+'thugs'='nothugs'
'nothugs' with letters rearranged gives 'SHOTGUN'.
'with' acts as a link.
(Other definitions for shotgun that I've seen before include "Smooth-bore weapon" , "Firearm used at short range - kind of wedding" , "No thugs (anag) - weapon" , "piece" , "arm" .)