See a nerd performing romantic song (8)
I believe the answer is:
serenade
'romantic song' is the definition.
'see a nerd performing' is the wordplay.
'performing' indicates anagramming the letters.
'see'+'a'+'nerd'='seeanerd'
'seeanerd' is an anagram of 'SERENADE'.
(Other definitions for serenade that I've seen before include "Murder" , "Piece sung beneath beloved's window" , "It's played or sung at a lover's window" , "Evening music (played outside woman's house)" , "Song to a lover" .)