"Starting all over . . ." (4,2,6,3)
I believe the answer is:
back to square one
'starting all over' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for back to square one that I've seen before include "Ready to start all over again" , "when you'd gone right round the board" , "Illegal pawn move made" , "having another go at solving 1 ac?" , "no further forward?" .)