Reversal of direction (1-4)
I believe the answer is:
u-turn
'reversal of direction' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for u-turn that I've seen before include "drastic change" , "Sudden reversal" , "Complete reverse movement as by car" , "Complete reverse of car on public road" , "Embarrassing reversal" .)