Moved back and forth or sideways (6)
I believe the answer is:
rocked
'moved back and forth or sideways' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for rocked that I've seen before include "Move to and fro, as with cradle" , "Moved back and forth or sideways" , "Shook, swayed" , "Startled, shaken" , "Swayed or shaken - or danced vigorously" .)