Instant game, crazy and played without singing (12)
I believe the answer is:
instrumental
'played without singing' is the definition.
(as in instrumental music)
'instant game crazy' is the wordplay.
'instant' becomes 'inst' (synonyms).
'game' becomes 'RU' (rugby union).
'crazy' becomes 'mental' (mentally ill).
'inst'+'ru'+'mental'='INSTRUMENTAL'
'and' is the link.
(Other definitions for instrumental that I've seen before include "Like a musical piece - it's of help" , "case" , "Having some responsibility - not vocal" , "Important" , "doing without singers" .)