So the three misbehaving are given a warning (9)
I believe the answer is:
therefore
'so' is the definition.
(I've seen this before)
'the three misbehaving are given a warning' is the wordplay.
'misbehaving' indicates anagramming the letters.
'are given' is a charade indicator (letters next to each other).
'a warning' becomes 'fore' (I've seen this before).
'three' with letters rearranged gives 'there'.
'there'+'fore'='THEREFORE'
(Other definitions for therefore that I've seen before include "In consequence" , "Ergo" , "Consequently - for that reason" , "has a triangular formation in maths?" , "It follows" .)