The hobbies of father's days (8)
I believe the answer is:
pastimes
'the hobbies' is the definition.
(I've seen this before)
'father's days' is the wordplay.
'father's' becomes 'pa's' (pa can mean dad or father).
'days' becomes 'times' (I can't explain this - if you can you should believe this answer much more).
'pas'+'times'='PASTIMES'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for pastimes that I've seen before include "Hobbies or diversions" , "leisure activities" .)