Some toper in pub interfered with mate (8,6)
I believe the answer is:
opposite number
'mate' is the definition.
(both can mean an associate)
'some toper in pub interfered with' is the wordplay.
'interfered with' indicates an anagram.
'some'+'toper'+'in'+'pub'='sometoperinpub'
'sometoperinpub' anagrammed gives 'OPPOSITE NUMBER'.
(Other definitions for opposite number that I've seen before include "pal!" , "Counterpart" , "colleague elsewhere" , "Direct competitor" , "One of similar status" .)