Brisk musical movement (7)
'brisk musical movement' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for allegro that I've seen before include "Gaily, lively (music)" , "quickly found in bars?" , "musical term" , "At a brisk speed (music)" , "(In music) briskly" .)
(Other definitions for scherzo that I've seen before include "Fast movement (mus.)" , "Symphonic movement, may have trio" , "Form in music" , "(In music) a brisk and lively movement" , "Fast musical movement" .)