Attack from the rear to capture a Pacific island (4)
I believe the answer is:
guam
'pacific island' is the definition.
(I've seen this before)
'attack from the rear to capture a' is the wordplay.
'attack' becomes 'mug' (I've seen this before**).
'from the rear' shows that the letters should be reversed in order.
'to capture' indicates putting letters inside.
'mug' in reverse letter order is 'gum'.
'gum' enclosing 'a' is 'GUAM'.
(Other definitions for guam that I've seen before include "place in the Marianas" , "US island east of the Philippines" , "US unincorporated territory in the western Pacific" , "Largest of the Mariana Islands" , "NW Pacific island with large US base" .)