One not really responsible for scarecrow perhaps (3,2,5)
I believe the answer is:
man of straw
I believe this clue is a double definition.
'one not really responsible' is the first definition.
(someone taking a responsibility they can't deliver)
'scarecrow perhaps' is the second definition.
(scarecrows are made of straw)
'for' acts as a link.
(Other definitions for man of straw that I've seen before include "Person of no substance" , "one of little substance" , "Weak character" , "scarecrow?" , "Phoney" .)