For the first time at the Summer Olympics, basketball fans will have two disciplines to follow when a fast-paced, showy version of the traditional five-a-side game debuts in Tokyo. This new event may look familiar to anyone accustomed to hunting for pickup games on their neighborhood courts: Teams will compete in 10-minute, first-to-21-point games where flashy shooters are rewarded and play will move at breakneck speed, in part because the court is smaller. Sound fun? It’s meant to be — the introduction of three-on-three basketball is part of the never-ending effort to attract younger viewers to the Games.