Section of orchestra in main pit, possibly (7)
I believe the answer is:
'section of orchestra' is the definition.
(instruments in an orchestra)
'main pit possibly' is the wordplay.
'possibly' is an anagram indicator.
'mainpit' is an anagram of 'TIMPANI'.
'in' acts as a link.
(Other definitions for timpani that I've seen before include "Something making drumming noise" , "Those beaten" , "orchestra members" , "set of instruments" , "PM, I ain't (anag.)" .)