Crowd in Guantanamo Bay (3)
I believe the answer is:
mob
'crowd' is the definition.
(mob can mean a crowd of people)
'in guantanamo bay' is the wordplay.
'in' says the answer is hidden in the clue.
'MOB' can be found hidden inside 'guantanamo bay'.
(Other definitions for mob that I've seen before include "Mafiosi" , "press round" , "Rowdy lot" , "Unruly crowd" , "Unruly lot" .)