Label written in stages (3)
I believe the answer is:
tag
'label' is the definition.
(I know that label can be written as tag)
'written in stages' is the wordplay.
'written in' says the answer is hidden in the clue.
'TAG' is hidden in the letters of 'stages'.
(Other definitions for tag that I've seen before include "Label - children's game" , "day in Berlin" , "Name" , "Children's chasing game" , "Identity disc" .)