Expel chaps before start of term for behaviour (10)
I believe the answer is:
deportment
'behaviour' is the definition.
('deportment' can be a synonym of 'behaviour')
'expel chaps before start of term' is the wordplay.
'expel' becomes 'deport' (deporting is a kind of expelling**).
'chaps' becomes 'men' (I've seen this before).
'before' is a charade indicator (letters next to each other).
'start of' suggests taking the first letters.
The initial letter of 'term' is 't'.
'deport'+'men'+'t'='DEPORTMENT'
'for' acts as a link.
(Other definitions for deportment that I've seen before include "(Physical) bearing" , "Conduct" , "Manners" , "Behaviour - bearing" , "Way of standing or walking" .)