Step on it in haste (5)
I believe the answer is:
hurry
I believe this clue is a double definition.
'step on it' is the first definition.
(I've seen this in another clue)
'haste' is the second definition.
(I know that haste can be written as hurry)
'in' is the link.
(Other definitions for hurry that I've seen before include "Make haste" , "Be quick" , "Haste(n)" , "Get a move on" , "Rush" .)