Hecklers' chorus (4)
I believe the answer is:
'hecklers' chorus' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for boos that I've seen before include "Sounds of disapproval" , "Catcalls" , "Shouts of disapproval" , "Shows disapproval" , "Shouts of derision" .)