The three color variants of them act as a booby prizes in every set. But what are they?
With so many toy capsules being based on something from SEGA games it's natural to look for their roots there. Especially with one of the other famous booby prizes called Binsbein, wich is a type of enemy from Space Harrier. They have a peculiar line running around the middle, giving the impression of opening in some way. However, the Super Balls come from a different background. Simply put, they're bouncy balls.
They aren't any kind of generic bouncy ball though. They are made from a very specific rubber recipe called Zectron, wich was originally invented by Norman Stingley in 1964. He then pitched the idea to the company Wham-O wich brought them to the market after more than a year of testing under the brand name "Super Ball". And the line around them is actually just a seam from production, where the two halves of the mold meet.
|An original 1965 Wham-O Super Ball|
The Super Ball turned into a big fad in it's early years because of it's very good coefficient of restitution, wich gave them superior bounciness over the competition. The name became a synonym for bouncy balls eventually. They were so widespread in the US that they even made the basis of one of the most well known sporting events in the word: the Super Bowl.
Of course over time, as more complex toys we're invented and electronics took over the Super Ball lost in popularity. But Wham-O still manufactures them and sells them under the Super Ball name to this very day.
|A Japanese Super Ball Vending Machine|
Of course all sorts of bouncy balls found their way into vending machines, with many being filled with nothing but those rubber objects. Makes perfect sense that they can be found in the toy capsule machines in Shenmue. I can't say for certain if the original Super Ball by Wham-O made its way to Japan but at least some derivitives did. The term "Super Ball" is definately known in Japan and there is even a game called "Super Ball Scooping" where a lot of them are put in a tub filled with water. You only get a flat, round piece of paper supported by a piece of metal to scoop them up, with the challenge to get as many as possible before the paper gets too wet and tears.