Fancy a round, stopping out (6)
I believe the answer is:
notion
'fancy a round stopping out' is the definition.
'notion' can be an answer for 'fancy' (both can mean an idea or whim). I'm unsure of the 'a round stopping out' bit.
'fancy a round stopping out' is the wordplay.
'fancy a round' becomes 'o' (I am not sure about this - if you are sure you should believe this answer much more).
'stopping' is an insertion indicator (inserted letters stop or plug a gap).
'out' becomes 'not in' (I've seen this before).
'o' put inside 'notin' is 'NOTION'.
Can you help me to learn more?
(Other definitions for notion that I've seen before include "Vague idea or opinion" , "Vague or whimsical idea" , "Caprice" , "Idea or whim" , "Idea or fancy" .)