The best part of a play (4)
I believe the answer is:
lead
This clue is a double definition.
'the best part' is the first definition.
(I've seen this in another clue)
'a play' is the second definition.
(I know that lead is a type of turn)
'of' acts as a link.
(Other definitions for lead that I've seen before include "Guide, direct" , "Be in charge of; metal" , "Guide the heavy metal" , "shot maybe" , "Starring role - kind of pencil" .)