King headed off in underpants to press conferences (9)
I believe the answer is:
briefings
'underpants to press conferences' is the definition.
I can't judge whether this definition defines the answer.
'king headed off in' is the wordplay.
'headed' means to remove the first letter (head can mean to remove the top from something).
'off' becomes 'briefs' (I can't justify this - if you can you should believe this answer much more).
'in' is an insertion indicator.
'king' with its initial letter taken off is 'ing'.
'ing' inserted within 'briefs' is 'BRIEFINGS'.
Can you help me to learn more?
(Another definition for briefings that I've seen is " Instructions".)