At United Nations, Australian leader reportedly sports these catching them by surprise (8)
I believe the answer is:
unawares
'by surprise' is the definition.
(I've seen this in another clue)
'at united nations australian leader reportedly' is the wordplay.
'at' is a charade indicator (letters next to each other).
'united nations' becomes 'UN' (abbreviation).
'australian' becomes 'A' (common abbreviation).
'leader reportedly' becomes 'wares' (I can't explain this - if you can you should believe this answer much more).
'un' put next to 'a' is 'una'.
'una'+'wares'='UNAWARES'
'sports these catching them' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for unawares that I've seen before include "Not expecting" , "without realising" , "Unexpectedly, without noticing in new auras" , "Unexpectedly - suddenly" , "Without knowledge of the situation" .)