Soundly barricade political group (4)
I believe the answer is:
bloc
'political group' is the definition.
(I've seen this before)
'soundly barricade' is the wordplay.
'soundly' shows a homophone (sound like).
'barricade' becomes 'block' ('block' can be a synonym of 'barricade').
'block' sounds like 'BLOC'.
(Other definitions for bloc that I've seen before include "multinational group" , "Alliance of nations" , "Group with a common policy" , "A number of countries" , "Political coalition" .)