Strike back before number making complaint (7)
I believe the answer is:
malaria
'complaint' is the definition.
(malaria is a kind of disease)
'strike back before number' is the wordplay.
'strike' becomes 'lam' (to 'lam' means to hit hard).
'back' says the letters should be written in reverse.
'before' is a charade indicator (letters next to each other).
'number' becomes 'aria' (I have seen 'Operatic number ' mean 'aria' so perhaps 'number' could also mean 'aria').
'lam' written backwards gives 'mal'.
'mal'+'aria'='MALARIA'
'making' is the link.
(Other definitions for malaria that I've seen before include "Disease from bites by infected mosquitos" , "Protozoal disease" , "Disease carried by mosquitoes" , "Fever-inducing disease" , "Mosquito-transmitted disease" .)