Behaved badly (5,2)
I believe the answer is:
acted up
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">behaved badly</span>' is the definition.<br/ ><span class="explanation-format__explanation">(acting up is a kind of behaving badly)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for acted up that I've seen before include "Behaved badly" , "carried on" .)