Excellent team run by peer (9)
I believe the answer is:
classmate
'peer' is the definition.
(I've seen this in another clue)
'excellent team run by' is the wordplay.
'excellent' becomes 'class' (I've seen this before).
'run' indicates an anagram.
'by' is a charade indicator (letters next to each other).
'team' with letters rearranged gives 'mate'.
'class'+'mate'='CLASSMATE'
(Other definitions for classmate that I've seen before include "someone from school?" , "Schoolfellow" , "one of the others being in form" , "Fellow pupil" , "Fellow student" .)