Foolish for native mother to leave (7)
I believe the answer is:
idiotic
'foolish' is the definition.
(I've seen this before)
'native mother to leave' is the wordplay.
'native' becomes 'idiomatic' (idiomatic describes native use of language).
'mother' becomes 'ma' (Ma is another word for mother or mum).
'to leave' is a deletion indicator.
'idiomatic' with 'ma' taken away is 'IDIOTIC'.
'for' acts as a link.
(Other definitions for idiotic that I've seen before include "Fatuous" , "Absurd, crackbrained" , "without intelligence" , "Witless" , "Ridiculous" .)