Nigel, clumsy chap, careless (9)
I believe the answer is:
negligent
'careless' is the definition.
('negligent' can be similar in meaning to 'careless')
'nigel clumsy chap' is the wordplay.
'clumsy' is an anagram indicator.
'chap' becomes 'gent' (I've seen this in other clues**).
'nigel' with letters rearranged gives 'negli'.
'negli'+'gent'='NEGLIGENT'
(Other definitions for negligent that I've seen before include "Careless of duties" , "sloppy" , "Not minding" , "Of the study of insects" , "Not taking due care" .)