Turned sinister in front of an audience (4)
I believe the answer is:
live
'in front of an audience' is the definition.
(as in live music)
'turned sinister' is the wordplay.
'turned' says the letters should be written in reverse.
'sinister' becomes 'evil' (similar in meaning).
'evil' reversed gives 'LIVE'.
(Other definitions for live that I've seen before include "Of TV programme, seen while taking place" , "Dwell" , "Electrically charged" , "Heard or seen as the event takes place and not from a recording" , "Eg, from Kingston" .)