Spiteful comment about rising American composer (6)
I believe the answer is:
barber
'american composer' is the definition.
(Samuel Barber)
'spiteful comment about rising' is the wordplay.
'spiteful comment' becomes 'barb' (I've seen this in another clue).
'about' becomes 're' ('re' means regarding or about).
'rising' shows that the letters should be reversed in order (going up in a down clue).
're' back-to-front is 'er'.
'barb'+'er'='BARBER'
(Other definitions for barber that I've seen before include "Hairdresser who also shaves beards" , "One who cuts hair" , "Hair cutter" , "Rossini opera 'The ...... of Seville'" , "responsible for Hair?" .)