A regulation NBA basketball is 9" in diameter, a regulation NBA hoop is 18" in diameter. It would be a squeek but it could happen. Would have to be a Harlem Globetrotters game tho. Da da da, ta dadadadadahhh, sweet Georgis Brown. Ta da da da...

Here is a pdf of a hoop from a basketball hoop manufacturer: http://www.draperinc.com/images/Basketball/CADS/PDFs/A0576_04.pdf So the inside ID of the basketball hoop is indeed without question 18” (This of course is nominal and does not include tolerances… Uhm makes you think, however tolerance for that type and size of product is +/- .030 easily). Everywhere I read, a full size regulation ball has a circumference of 29.5 - 30” (which would imply some form of tolerance) and a diameter of 9” (which has no tolerance associated with it). Now, comes the equation: circumference = diameter * pie or diameter = circumference/pie Pie of course is approximately 3.14…, therefore one or both of those numbers have been rounded. If you divide 29.5/3.14 = 9.37, if you divide 30/3.14 = 9.55, this is a minimum 4% error of a 9” diameter ball (Also note both of those numbers are greater than 9 and neither of those numbers when multiplied by two are 18” or less). Now if we multiply 9*3.14 = 28.26, this means that if the ball is 9” in diameter than this is over one inch less than the regulation circumference. This is a minimum 5% error. So after inflating a basketball to its regulation size, which number is used to measure the size? According to the USA Basketball webpage, all measurements are made to the circumference. The smallest of which is the NBA @29.5”. So the smallest diameter is 9.37” http://www.usabasketball.com/rules/rules.html Size of Basketball Maximum Circumference 78 cm (30.7") Around channels 29 1/2" to 29 3/4" Across channels 29 5/8" to 29 7/8" Maximum Circumference 30" Seams 1/4" Max. Therefore, unless the balls are forced or not completely pumped they cannot fit through side by side at the same time, so there… However, these numbers are for a full sized regulation Basketball. There are "intermediate" sized balls (used for junior players) which may indeed fit through a hoop at the same time without any externally applied force...

no, because a regulation basketball is more than half the diameter of a regualtion hoop.