It's almost a toss-up whether he's sozzled! (3)
I believe the answer is:
sot
'whether he's sozzled' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'it's almost a toss-up' is the wordplay.
'it's almost' means to remove the last letter (almost the whole word is kept).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'toss' with its last letter taken away is 'tos'.
'tos' backwards is 'SOT'.
Can you help me to learn more?
(Other definitions for sot that I've seen before include "drunk" , "Boozer" , "Lush" , "Habitual drunkard" , "A chronic drinker" .)