Chap left two articles outside (4)
I believe the answer is:
alan
'chap' is the definition.
(a chap named alan)
'left two articles outside' is the wordplay.
'left' becomes 'l' (common abbreviation).
'two articles' becomes 'aan' (article meaning part of speech: the, a etc.).
'outside' is an insertion indicator.
'l' placed within 'aan' is 'ALAN'.
(Other definitions for alan that I've seen before include "- Bennett, English actor, dramatist, writer" , "- Bates, - Bennett" , "A.A. Milne's first name" , "One of Robin Hood's men was - a Dale" , "-- Turing, mathematician" .)