Had quit the side (4)
I believe the answer is:
left
'side' is the definition.
(as opposed to right)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for left that I've seen before include "Socialist direction" , "Departed, went away" , "Vacated; political wing" , "One < side" , "The sinister side" .)