Very naughty boy outside a court, having arrived with large beast (8,5)
I believe the answer is:
bactrian camel
'large beast' is the definition.
'bactrian camel' can be an answer for 'beast'. I am unsure of the 'large' bit.
'very naughty boy outside a court having arrived' is the wordplay.
'very naughty boy' becomes 'Brian' (reference to Monty Python's Life of Brian).
'outside' is an insertion indicator.
'court' becomes 'ct' (abbreviation used in road names).
'having' says to put letters next to each other.
'arrived' becomes 'camel' (I can't justify this - if you can you should give a lot more credence to this answer).
'a'+'ct'='act'
'brian' enclosing 'act' is 'bactrian'.
'bactrian'+'camel'='BACTRIAN CAMEL'
'with' acts as a link.
(Other definitions for bactrian camel that I've seen before include "Two-humped creature" , "Humped animal" , "Two-humped animal" .)