United supporters backing confused situation (5)
I believe the answer is:
snafu
'confused situation' is the definition.
(I've seen this in another clue)
'united supporters backing' is the wordplay.
'united' becomes 'U' (abbreviation).
'supporters' becomes 'fans' (fan is a kind of supporter).
'backing' is a reversal indicator.
'u'+'fans'='ufans'
'ufans' backwards is 'SNAFU'.
(Other definitions for snafu that I've seen before include "in a bad state" , "Slangy acronym meaning in total confusion" , "Chaos (US slang)" , "Chaotic situation" , "Mess table" .)