Investigation of lariat rope-running heading to the West (6)
I believe the answer is:
report
'investigation' is the definition.
'of lariat rope-running heading to the west' is the wordplay.
'of' indicates the answer is hidden within the clue.
'to the west' is a reversal indicator (letters written right to left or \'east to west\').
'troper' is hidden in the letters of 'lariat rope running heading'.
'troper' written backwards gives 'REPORT'.
(Other definitions for report that I've seen before include "Statement of fact" , "Teacher's assessment" , "Complain about; noise" , "Announce; rumour" , "News item - sound of gun" .)