Do something in play (3)
I believe the answer is:
act
I believe this clue is a double definition.
'do something' is the first definition.
(I've seen this before)
'play' is the second definition.
('act' can be a synonym of 'play')
'in' acts as a link.
(Other definitions for act that I've seen before include "Do something (on stage?)" , "Assumed attitude" , "Take steps" , "Thing done" , "Do something, in a play?" .)