Barrack (6)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">barrack</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(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" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">barrack</span>' is the definition.<br/ ><span class="explanation-format__explanation">('barrack' can mean to jeer at or heckle)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for boo that I've seen before include "Exclamation to startle" , "Express noisy disapproval" , "get off!" , "Catcall" , "A shocking exclamation!" .)