Uplifting numbers at a musical performance (6)
I believe the answer is:
sonata
'musical performance' is the definition.
(I've seen this before)
'uplifting numbers at a' is the wordplay.
'uplifting' says the letters should be written in reverse.
'numbers' becomes 'nos' ('no' is an abbreviation for number).
'nos' written backwards gives 'son'.
'son'+'at'+'a'='SONATA'
(Other definitions for sonata that I've seen before include "Solo piano composition" , "just for one or two players?" , "Solo instrumental composition" , "Musical composition with three or more contrasting movements" , "A musical form" .)