Best man hugged by old friend (7)
I believe the answer is:
optimal
'best' is the definition.
('optimal' can be similar in meaning to 'best')
'man hugged by old friend' is the wordplay.
'man' becomes 'tim'.
'hugged by' is an insertion indicator (I've seen this in other clues).
'old friend' becomes 'opal' (I can't justify this - if you can you should give a lot more credence to this answer).
'tim' put inside 'opal' is 'OPTIMAL'.
Can you help me to learn more?
(Other definitions for optimal that I've seen before include "Am pilot being at best" , "Plot aim (anag) - most favourable" , "Most desirable" , "top, surprisingly" , "couldn't be better" .)