Did you know that two basketballs fit, side by side, through a basketball hoop? Eyeballing things like this is almost never close to right.

You can probably cram them through since they are flexible, but they wouldn't fit without some force; a regulation rim is 18 inches inside diameter and a basketball 9.5 inches diameter.

Good catch. I saw this demonstrated in grade school, where they were probably using size 6 balls. Nevertheless, most people think it's not even close.