Jumping bail I find an excuse (5)
I believe the answer is:
alibi
'an excuse' is the definition.
(excuse given by a suspect in an investigation)
'jumping bail i' is the wordplay.
'jumping' indicates an anagram.
'bail' with letters rearranged gives 'alib'.
'alib'+'i'='ALIBI'
'find' acts as a link.
(Other definitions for alibi that I've seen before include "Defence in court" , "Proof of being somewhere else at the time" , "Pretext; court excuse" , "Story confirming innocence" , "Defence used by an accused person" .)