Back final runner clearing the last at Perth (7)
I believe the answer is:
endorse
'back' is the definition.
(back can mean to support or endorse)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for endorse that I've seen before include "Approve - support" , "Favour" , "Put penalty points on (a driving licence)" , "Add one's authority to" , "Give public approval of (something)" .)