Poles meeting inside trail back (7)
I believe the answer is:
sponsor
'back' is the definition.
(I've seen this before)
'poles meeting inside trail' is the wordplay.
I cannot really see how this works, but
'poles' could be 'ns' (north and south poles) and 'ns' is located in the answer.
'trail' could be 'spoor' (spoor is a kind of trail) and 'spoor' is present in the leftover letters.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for sponsor that I've seen before include "One who pays costs for event" , "A godfather or patron" , "Provide finance for" , "Pledge money" , "Godparent at a baptism" .)