Musical composition has right person on pitch (6)
I believe the answer is:
scorer
'person on pitch' is the definition.
'scorer' can be an answer for 'person' (scorer is a kind of person). I'm not certain of the 'on pitch' bit.
'musical composition has right' is the wordplay.
I cannot quite see how this works, but
'composition' could be 'score' (score is a kind of composition) and 'score' is located in the answer.
'right' could be 'r' (common abbreviation) and 'r' is found in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for scorer that I've seen before include "Footballer having netted" , "Sir, not one without heart as a" , "One gaining points" , "Cricket official" , "He puts the ball in the net" .)