Charity do back in Malaga (4)
I believe the answer is:
gala
'charity do' is the definition.
(I've seen this in another clue)
'back in malaga' is the wordplay.
'back' says the letters should be written backwards.
'in' indicates the answer is hidden within the clue.
'alag' is hidden in the letters of 'malaga'.
'alag' in reverse letter order is 'GALA'.
(Other definitions for gala that I've seen before include "Public party" , "Swimming competition" , "Carnival, celebration" , "field day" , "Festive celebration" .)