Upset a large bear, creating fuss (6)
I believe the answer is:
hoopla
'fuss' is the definition.
(I've seen this before)
'upset a large bear' is the wordplay.
'upset' is a reversal indicator.
'large' becomes 'L' (eg in clothes sizes).
'bear' becomes 'pooh' (Winnie the Pooh).
'a'+'l'+'pooh'='alpooh'
'alpooh' in reverse letter order is 'HOOPLA'.
'creating' acts as a link.
(Other definitions for hoopla that I've seen before include "Throwing game where prizes aimed for" , "Game in which rings are thrown over objects in order to win them" , "Fairground stall attraction" , "fair prize at this" , "Fairground throwing game" .)