A KO shot? (5)

I believe the answer is:
outer
'shot?' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for outer that I've seen before include "Surrounding" , "External; peripheral" , "Ring for double scores on a dartboard" , "Exterior or external, like space" , "Ring furthest from the bullseye" .)
