Arranging bail, one has a legal defence (5)
I believe the answer is:
alibi
'a legal defence' is the definition.
(I've seen this before)
'arranging bail one' is the wordplay.
'arranging' indicates anagramming the letters.
'one' becomes 'i' (Roman numeral).
'bail' anagrammed gives 'alib'.
'alib'+'i'='ALIBI'
'has' is the link.
(Other definitions for alibi that I've seen before include "Timely excuse" , "It shows one wasn't at crime scene" , "Story confirming innocence" , "Proof of being somewhere else at the time" , "I bail (anag.)" .)