Possibly rail at the rope (6)
I believe the answer is:
lariat
'the rope' is the definition.
(lariat is a kind of rope)
'possibly rail at' is the wordplay.
'possibly' indicates an anagram.
'rail' is an anagram of 'lari'.
'lari'+'at'='LARIAT'
(Other definitions for lariat that I've seen before include "Long noosed rope for catching animals" , "Long noosed rope used to catch animals" , "A cowboy's rope with noose" , "Cowboy's rope, lasso" , "Rope for the cowboy" .)