Father backed mother, say - that's obvious (8)
I believe the answer is:
apparent
'that's obvious' is the definition.
('apparent' can be similar in meaning to 'obvious')
'father backed mother' is the wordplay.
'father' becomes 'pa' (pa is a kind of father).
'backed' shows that the letters should be reversed in order.
'mother' becomes 'parent' (I've seen this in other clues).
'pa' back-to-front is 'ap'.
'ap'+'parent'='APPARENT'
'say' acts as a link.
(Other definitions for apparent that I've seen before include "Seeming real or true" , "Conspicuous" , "Obvious, evident" , "Quite obvious and clear" , "Readily perceived" .)