Cad’s cue to involve defendant (7)
I believe the answer is:
'defendant' is the definition.
'cad's cue to involve' is the wordplay.
'to involve' indicates anagramming the letters.
'cadscue' is an anagram of 'ACCUSED'.
(Other definitions for accused that I've seen before include "Levelled a charge against" , "Defendant appearing on a criminal charge" , "Indicted" , "Incriminated" , "One tried" .)