Barrack (3)
'barrack' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for heckle that I've seen before include "Shout down (a politician)" , "Shout abuse at, a speaker say" , "Mock or harangue speaker from crowd" , "Harass a speaker" , "Taunt" .)
'barrack' is the definition.
('barrack' can mean to jeer at or heckle)
This is the entire clue.
(Other definitions for boo that I've seen before include "Exclamation to startle" , "Express noisy disapproval" , "get off!" , "Catcall" , "A shocking exclamation!" .)