Here's a picture of what that looks like from IPDB. I've not seen a captive ball area designed like this before and can see why that gate looking thing would take a lot of abuse and break. If you hit the gate on the right, does that fling the captive ball up to the target? If it does, I can see why yours is missing as it probably broke. I probably would leave it out as it doesn't seem like a good design to me.
image-4 (resized).jpg