Class in gym excited, enthralled by outstanding teacher (9)
I believe the answer is:
pedagogue
'teacher' is the definition.
(I've seen this before)
'class in gym excited enthralled by outstanding' is the wordplay.
'class in gym' becomes 'PE' (Physical Education).
'excited' becomes 'agog' (similar in meaning).
'enthralled by' means one lot of letters goes inside another ('enthral' can mean 'capture').
'outstanding' becomes 'due' (an outstanding debt is due).
'agog' placed within 'due' is 'dagogue'.
'pe'+'dagogue'='PEDAGOGUE'
(Other definitions for pedagogue that I've seen before include "Dogmatic teacher" , "Strict teacher" , "Educator of young people" , "Schoolmaster" .)