Hurt leg - I knocked over Greek character's organ (9)
I believe the answer is:
harmonium
'organ' is the definition.
(synonyms)
'hurt leg i knocked over greek character's' is the wordplay.
'hurt' becomes 'harm' (synonyms).
'leg' becomes 'on' (cricket term, fielding positions).
'knocked over' says the letters should be written in reverse.
'greek character' becomes 'mu' (letter from the Greek alphabet).
'mu' written backwards gives 'um'.
'harm'+'on'+'i'+'um'='HARMONIUM'
(Other definitions for harmonium that I've seen before include "Keyboard instrument - a minor hum (anag)" , "Pedalled-bellows instrument" .)