Unlucky to be badly cast as a leading actor (3-7)

'unlucky' is the definition.
(I know that unlucky can be written as ill-starred)

'badly cast as a leading actor' is the wordplay.
I cannot really see how this works, but
'badly' could be 'ill' (eg in ill-advised) and 'ill' is found within the answer.
'a' is within the answer.
This explanation may well be incorrect...

'to be' acts as a link.

Can you help me to learn more?