Actors veto gin cocktail in deciding ballot (7,4)
I believe the answer is:
casting vote
'deciding ballot' is the definition.
'casting vote' can be an answer for 'ballot' (casting vote is a kind of ballot). I'm not sure about the 'deciding' bit.
'actors veto gin cocktail' is the wordplay.
'actors' becomes 'cast' (group of actors).
'cocktail' indicates anagramming the letters.
'veto'+'gin'='vetogin'
'vetogin' is an anagram of 'ingvote'.
'cast'+'ingvote'='CASTING-VOTE'
'in' is the link.
Can you help me to learn more?
(Other definitions for casting vote that I've seen before include "Deciding opinion" , "One given to resolve deadlock" , "This decides it" , "Taking part in election" .)