Revealing close call supporting United? (10)
I believe the answer is:
unearthing
'revealing' is the definition.
(to unearth is to discover or reveal)
'close call supporting united?' is the wordplay.
'close call' becomes 'near thing' (I've seen this before).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'united?' becomes 'U' (abbreviation).
'nearthing' after 'u' is 'UNEARTHING'.
(Other definitions for unearthing that I've seen before include "Revealing" , "Discovering" .)