Party game has raced off (8)
I believe the answer is:
charades
'party game' is the definition.
(I've seen this before)
'has raced off' is the wordplay.
'off' indicates an anagram.
'has'+'raced'='hasraced'
'hasraced' anagrammed gives 'CHARADES'.
(Other definitions for charades that I've seen before include "Miming parlour game" , "Games like this" , "Game in which answers are acted out" , "Guessing game where words are acted out" , "Miming games" .)