Legal defence, some fib I later retracted (5)
I believe the answer is:
alibi
'legal defence' is the definition.
(I've seen this before)
'some fib i later retracted' is the wordplay.
'some' says the answer is hidden in the clue (some parts of the word are used).
'retracted' shows that the letters should be reversed in order.
'ibila' is hidden in the letters of 'fib i later'.
'ibila' reversed gives 'ALIBI'.
(Other definitions for alibi that I've seen before include "Legal defence - was elsewhere" , "Fact of being elsewhere (legal)" , "Legal proof of innocence" , "Answer to charge - was somewhere else" , "Defence against accusation - was somewhere else" .)