After losing case, tyrant has to employ advocate (7)
I believe the answer is:
Here is my best explanation:
'advocate' is the definition.
'after losing case tyrant has to employ' is the wordplay.
I cannot really see how this works, but
'employ' could be 'use' ('use' can be a synonym of 'employ') and 'use' is present in the answer.
This may be the basis of clue (or it may be nonsense).