For starters, this upstart tried to introduce section where all instruments play together (5)
I believe the answer is:
tutti
'play together' is the definition.
(I've seen this before)
'for starters this upstart tried to introduce' is the wordplay.
'for starters' says to take the initial letters.
The first letters of 'this upstart tried to introduce' is 'TUTTI'.
'section where all instruments' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for tutti that I've seen before include "Section for all musicians" , "- - -frutti" , "Composer of Carmina Burana" , "Orchestral passage" , "Piece together" .)