Non-professionals misbehaving meanly (6)
I believe the answer is:
laymen
'non-professionals' is the definition.
(I've seen this before)
'misbehaving meanly' is the wordplay.
'misbehaving' indicates an anagram.
'meanly' is an anagram of 'LAYMEN'.
(Other definitions for laymen that I've seen before include "Male parishioners" , "Non-professionals" , "Amateur" , "Namely, not being priests or professionals" , "amateurs" .)