Step to get rid of a commotion (4)
I believe the answer is:
Here is my best explanation:
'commotion' is the definition.
(stir is a kind of commotion)
'step to get rid of a' is the subsidiary indication.
'step' becomes 'stair' ('stair' can be a synonym of 'step').
'to get rid of' suggests deleting specific letters.
'stair' with 'a' removed is 'stir'.
(Other definitions for stir that I've seen before include "cause trouble?", "Cause trouble", "More very slightly, or agitate", "Detention centre", "Stimulate; prison", "Sensation", "jug", "Whisk, blend", "Move slightly" and "Slight movement".)