Continentals uncommonly sure about Australian in competition (9)
I believe the answer is:
europeans
'continentals' is the definition.
(I've seen this before)
'uncommonly sure about australian in competition' is the wordplay.
'uncommonly' is an anagram indicator.
'about' indicates putting letters inside.
'australian' becomes 'A' (common abbreviation).
'in' means one lot of letters goes inside another.
'competition' becomes 'open' (open is a kind of competition).
'sure' is an anagram of 'eurs'.
'a' put inside 'open' is 'opean'.
'eurs' going around 'opean' is 'EUROPEANS'.
(Other definitions for europeans that I've seen before include "Continentals" , "Frenchmen, Irishwomen, for instance" , "Irish and French people, say" , "The French and Italians, say" .)