Make final catch in a low position (4,4)
I believe the answer is:
nail down
'make final' is the definition.
('nail down' can be a synonym of 'make final')
'catch in a low position' is the wordplay.
I cannot really understand how this works, but
'catch' could be 'nail' (I've seen this before) and 'nail' is found within the answer.
'low' could be 'down' ('down' can be a synonym of 'low') and 'down' is found in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for nail down that I've seen before include "Bind to a promise, using hammer and metal pin" , "Identify (something) precisely" , "Firmly fix" , "An old win (anag.)" , "make final" .)