They're knocked down in alleys (8)
I believe the answer is:
ninepins
'alleys' is the definition.
The answer and definition can be both man-made objects as well as being plural nouns.
Perhaps you can see a link between them that I can't see?
'they're knocked down in' is the wordplay.
I cannot quite understand how this works, but
'in' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for ninepins that I've seen before include "Bowling game" , "Bowling targets" , "Skittles (IX, not V)" , "Form of skittles" , "Skittles, IX objects to be knocked down" .)