Reckless one — drop out (8)
I believe the answer is:
tearaway
'reckless one' is the definition.
'drop out' is the wordplay.
'drop' becomes 'tear' (I've seen this before**).
'out' becomes 'away' ('away' can be a synonym of 'out').
'tear'+'away'='TEARAWAY'
(Other definitions for tearaway that I've seen before include "Rough" , "Might I stir" , "Unruly youth" , "Unruly, impetuous person" , "Hooligan" .)