Have advantage over United in 0-0? (5)
I believe the answer is:
outdo
'have advantage over' is the definition.
'united in 0-0' is the wordplay.
'united' becomes 'utd' (common abbreviation as in names of sports teams).
'in' is an insertion indicator.
'0 0' becomes 'OO' (resembles 00).
'utd' inserted into 'oo' is 'OUTDO'.
(Other definitions for outdo that I've seen before include "Defeat" , "Beat" , "Cap" , "Eclipse" , "Perform better than another" .)