Crustacean loose in KGB car (4,4)
I believe the answer is:
king crab
'crustacean' is the definition.
(king crab is a kind of crustacean)
'loose in kgb car' is the wordplay.
'loose' indicates an anagram (letters are loosened from their original positions).
'in'+'kgb'+'car'='inkgbcar'
'inkgbcar' is an anagram of 'KING-CRAB'.
(Other definitions for king crab that I've seen before include "Marine creature" , "seafood restaurant order" , "Large crustacean" .)