Facing one's mate on location (8)
I believe the answer is:
opposite
'facing' is the definition.
(as in two things facing each other)
'one's mate on location' is the wordplay.
'one's mate' becomes 'oppo' (term for a friend or colleague).
'on' says to put letters next to each other.
'location' becomes 'site' (site is a kind of location).
'oppo'+'site'='OPPOSITE'
(Other definitions for opposite that I've seen before include "Totally different; facing" , "reverse, in fact" , "Converse" , "Adverse" , "Rival" .)