V sign America’s leader deployed at borders (7)
I believe the answer is:
against
'v' is the definition.
(v means versus in sports fixtures)
'sign america's leader deployed at borders' is the wordplay.
'leader' suggests taking the first letters.
'deployed' is an anagram indicator.
'borders' means one lot of letters goes inside another (inserted letters are bordered by others).
The initial letter of 'americas' is 'a'.
'sign'+'a'='signa'
'signa' is an anagram of 'gains'.
'gains' inserted inside 'at' is 'AGAINST'.
(Other definitions for against that I've seen before include "Not supporting" , "on the other side" , "Opposing" , "V" , "Placed in direct contact with" .)