Blot on the character of a chap getting out of line (5)
I believe the answer is:
stain
'line' is the definition.
(thesaurus)
'blot on the character of a chap getting' is the wordplay.
'blot on the character of' becomes 'i' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a chap' becomes 'Stan'.
'getting' means one lot of letters goes inside another.
'i' placed within 'stan' is 'STAIN'.
'out of' acts as a link.
Can you help me to learn more?
(Other definitions for stain that I've seen before include "Colour, dye" , "Discoloration" , "Unsightly mark" , "Spot - shame" , "Discolouration" .)