Defence starts to address legal issues behind injunction (5)
I believe the answer is:
alibi
'defence' is the definition.
(alibi is a kind of defence)
'starts to address legal issues behind injunction' is the wordplay.
'starts to' says to take the initial letters.
The first letters of 'address legal issues behind injunction' is 'ALIBI'.
(Other definitions for alibi that I've seen before include "Lawyer's weapon, Latin for 'elsewhere'" , "Evidence one was not present" , "Plea of absence" , "that gets him off the hook?" , "Defence of being elsewhere at time of crime" .)