Chicken crossing a road? Step on it (6)
I believe the answer is:
hasten
'step on it' is the definition.
(I've seen this in another clue)
'chicken crossing a road?' is the wordplay.
'chicken' becomes 'hen' (hen is a kind of chicken).
'crossing' indicates putting letters inside.
'road?' becomes 'st' ().
'a'+'st'='ast'
'hen' enclosing 'ast' is 'HASTEN'.
(Other definitions for hasten that I've seen before include "Be quick to do something" , "Travel with expedition" , "Rush" , "Hurry up in old-fashioned way" , "Hurry along" .)