Novel newly penned by Stallone is carelessly done (8)
I believe the answer is:
slovenly
'carelessly done' is the definition.
(something slovenly is haphazardly done)
'novel newly penned by stallone' is the wordplay.
'newly' is an anagram indicator.
'penned by' indicates putting letters inside.
'stallone' becomes 'sly' (nickname for Sylvester Stallone).
'novel' is an anagram of 'ovenl'.
'ovenl' inserted inside 'sly' is 'SLOVENLY'.
'is' acts as a link.
(Other definitions for slovenly that I've seen before include "Habitually dirty and unkempt" , "Like a slob" , "Disorganised" , "messy state" , "Dirty and slipshod" .)