Off one's rocker (3)
I believe the answer is:
mad
'off one's rocker' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for mad that I've seen before include "like the March Hare" , "Angry or insane" , "Demented or excited or angry" , "Roused to anger" , "Aberrant" .)