Cheer up lad for the audience (4)
I believe the answer is:
buoy
'cheer up' is the definition.
(I've seen this in another clue)
'lad for the audience' is the wordplay.
'lad' becomes 'boy' (I've seen this in another clue).
'for the audience' shows a homophone (sound like) (how an audience might hear it).
'boy' is a homophone of 'BUOY'.
(Other definitions for buoy that I've seen before include "Sea-lane marker" , "keep from going under" , "dolphin" , "Navigational marker" , "Anchored (navigation) float" .)