Very well and appropriate baffle, as if playing inside (3,2,1,6)
I believe the answer is:
fit as a fiddle
'very well' is the definition.
(I've seen this before)
'appropriate baffle as if playing inside' is the wordplay.
I cannot quite see how this works, but
'appropriate' could be 'fit' (similar in meaning) and 'fit' is present in the answer.
'as' is within the answer.
This explanation may well be incorrect...
'and' acts as a link.
Can you help me to learn more?
(Other definitions for fit as a fiddle that I've seen before include "What item must do to go into violin case" , "Healthy (like a violin?)" , "Extremely healthy" , "Bouncing with health" , "Cheerful and well" .)