Best man gets old mate round (7)
I believe the answer is:
optimal
'best' is the definition.
(optimal means the best)
'man gets old mate round' is the wordplay.
'man' becomes 'Tim' (short for Timothy).
'gets' indicates putting letters inside.
'old mate round' becomes 'opal' (I am not sure about this - if you are sure you should believe this answer much more).
'tim' placed within 'opal' is 'OPTIMAL'.
Can you help me to learn more?
(Other definitions for optimal that I've seen before include "couldn't be better" , "Plot aim (anag) - most favourable" , "Am pilot being at best" , "best results" , "Ideal" .)