Shout of derision (7)
'shout of derision' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for catcall that I've seen before include "Noisy expression of disapproval" , "Mocking shout or whistle" , "Derisive call" , "Disapproving outcry" , "Express disapproval" .)
(Other definitions for boo that I've seen before include "I don't like that!" , "Exclamation of disapproval" , "I'm unimpressed" , "Disapproving sound" , "Frightening word (for a goose?)" .)