Besiege (8)
I believe the answer is:
blockade
'besiege' is the definition.
(I know that blockade is a type of besiege)
This is all the clue.
(Other definitions for blockade that I've seen before include "clampdown" , "The sealing off a place to prevent entry or exist" , "Besiege" , "Physical prevention of access" , "Seal off (a place)" .)