Watch first stage, quite something (3-6)
I believe the answer is:
eye-opener
'quite something' is the definition.
'watch first stage' is the wordplay.
I cannot really understand how this works, but
'watch' could be 'eye' (eye can mean to watch or look at) and 'eye' is found in the answer.
'first' could be 'opener' (I've seen this before) and 'opener' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for eye-opener that I've seen before include "Surprise revelation" , "Unexpected revelation" , "Something startling" , "Circumstances that brings surprise and enlightenment" , "Fact or circumstance that brings enlightenment and surprise" .)