King sheltered by a knight, aged chap (6)
I believe the answer is:
arnold
'chap' is the definition.
'king sheltered by a knight aged' is the wordplay.
'king' becomes 'r' (r is abbreviation for rex).
'sheltered by' is an insertion indicator.
'knight' becomes 'n' (chess).
'aged' becomes 'old' ('old' can be similar in meaning to 'aged').
'a'+'n'='an'
'r' inserted inside 'an' is 'arn'.
'arn'+'old'='ARNOLD'
(Other definitions for arnold that I've seen before include "Sir Malcolm -, English composer" , "Sir Malcolm -, composer (Bridge over the River Kwai)" , "-- Wesker, playwright" , "Matthew --, English poet" , "Matthew --; -- Bennett" .)