Chance in case of party game (6)
I believe the answer is:
plucky
'game' is the definition.
(thesaurus)
'chance in case of party' is the wordplay.
'chance' becomes 'luck' ('luck' can be a synonym of 'chance'**).
'in' indicates putting letters inside.
'case of' means to remove the middle letters (outsides of).
'party' with its middle removed is 'py'.
'luck' placed into 'py' is 'PLUCKY'.
(Other definitions for plucky that I've seen before include "Bold" , "Brave in English way" , "Game" , "stout" , "Courageous or feisty" .)