First part of play has touching effect (6)
I believe the answer is:
action
'effect' is the definition.
(action can mean a chemical effect)
'first part of play has touching' is the wordplay.
'first part of play' becomes 'Act I' (Act 1 in a play).
'has' is a charade indicator (letters next to each other).
'touching' becomes 'on'.
'acti'+'on'='ACTION'
(Other definitions for action that I've seen before include "It is said to speak louder than words" , "Take proceedings" , "Order to start shooting" , "Thing done; armed conflict" , "Operation - lawsuit" .)