Blunder initially riles boss (6)
I believe the answer is:
gaffer
'boss' is the definition.
(gaffer can informally mean a boss)
'blunder initially riles' is the wordplay.
I cannot quite see how this works, but
'blunder' could be 'gaffe' (gaffe is a kind of blunder) and 'gaffe' is found in the answer.
A single letter 'r' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for gaffer that I've seen before include "one prone to blunder socially?" , "Informal boss or foreman" , "Foreperson of a work squad" , "An old person" , "man in charge" .)