This classic toy is called Clackers (also known as Klackers or Popper).
It consists of two plastic balls connected by a flexible handle. You swing it up and down to make the balls “clack” together loudly — which is how it got its name.
Popular in the 70s and 80s, it was a simple but addictive playground toy. However, some versions were banned in certain places because the balls could crack or shatter if used too aggressively.
A fun piece of nostalgia that brings back memories for many!

