Support for one in litter (4,2)
I believe the answer is:
prop up
'support' is the definition.
(propping up is a kind of supporting)
'for one in litter' is the wordplay.
I cannot quite understand how this works, but
'for' could be 'pro' (as in being 'pro' or in favour of something) and 'pro' is found in the answer.
'litter' could be 'pup' (pupping is a kind of littering) and 'pup' is present in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for prop up that I've seen before include "Give financial backing" , "Underpin" , "Keep going" , "Support" .)