Spoil the walk (4)
I believe the answer is:
turn
This clue is a double definition.
'spoil' is the first definition.
(thesaurus)
'the walk' is the second definition.
(turn is a kind of walk)
(Other definitions for turn that I've seen before include "Move in a new direction" , "Go off - performance" , "fit" , "See 19" , "Revolve; act" .)