Juvenile teen's a clod, misbehaving (10)
I believe the answer is:
adolescent
'juvenile' is the definition.
('adolescent' can be a synonym of 'juvenile')
'teen's a clod misbehaving' is the wordplay.
'misbehaving' is an anagram indicator.
'teens'+'a'+'clod'='teensaclod'
'teensaclod' with letters rearranged gives 'ADOLESCENT'.
(Other definitions for adolescent that I've seen before include "At the stage between childhood and maturity" , "Developing" , "Young person" , "Person in child-adult transition" , "Immature" .)