Idle, following extremely casual father (6)
I believe the answer is:
cleric
'father' is the definition.
(I've seen this in another clue)
'idle following extremely casual' is the wordplay.
'idle' becomes 'eric' (I've seen this before).
'following' means one lot of letters go next to another.
'extremely' says to hollow out the word (remove centre letters) (only the extremes of the word are used).
'casual' with its centre removed is 'cl'.
'eric' put after 'cl' is 'CLERIC'.
(Other definitions for cleric that I've seen before include "Church minister" , "Clergyman" , "Person in holy orders" , "One is in religious orders" , "Church official" .)