Surrounded (5)
(Other definitions for cased that I've seen before include "Reconnoitred (sl.)" , "put in a box" , "Covered, protected; checked over (by robber)" , "Carefully inspected (for crime)" , "examined with intention to rob" .)
'surrounded' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for beset that I've seen before include "Encircled, attacked" , "Assail or attack on all sides" , "Surround and harass" , "Surrounded, under siege" , "besieged" .)