Shouts of disapproval (8)
(Other definitions for catcalls that I've seen before include "Derisive shouts" , "Shrill disapproving whistles of feline origin" , "Shrill whistles of disapproval - feline?" .)
'shouts of disapproval' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for boos that I've seen before include "Shouts of derision" , "Shows disapproval" , "Sounds of disapproval" , "Shouts of disapproval" , "Catcalls" .)