Figure to secure something often knocked down (7)
I believe the answer is:
'something often knocked down' is the definition.
I can't judge whether this definition defines the answer.
'figure to secure' is the wordplay.
'figure' becomes 'nine' (a number of figure).
'to secure' becomes 'pin' (pinning is a kind of securing).
Can you help me to learn more?
(Other definitions for ninepin that I've seen before include "target to knock over" , "Type of bowling" , "Skittle" , "game" , "What bowler tries to hit" .)