Not fully ready to enter the fog, being in the wrong role (7)
I believe the answer is:
miscast
'in the wrong role' is the definition.
(I've seen this in another clue)
'not fully ready to enter the fog' is the wordplay.
'not fully' means to remove the last letter.
'ready' becomes 'cash' (ready can informally mean cash).
'to enter' means one lot of letters goes inside another.
'the fog' becomes 'mist' (mist is a kind of fog).
'cash' with its last letter removed is 'cas'.
'cas' going within 'mist' is 'MISCAST'.
'being' acts as a link.
(Other definitions for miscast that I've seen before include "Of actor, unsuited to a role" , "part poorly chosen" , "in the wrong film?" , "having the wrong part" , "Given an unsuitable role" .)