Sandbag Basketball is a mini-game introduced in Super Smash Flash 2 as part of Arena. In this mode, up to four players are placed in an enclosed area, meaning they cannot get KO'd, with each one representing either the red or blue teams. Using the aforementioned Sandbag, players have to launch it into the opposing player's hoop for points, and the first team to reach the set number of points wins the match. Players can damage the Sandbag and as it gets more damaged, it will travel farther and will get launched faster, making it harder for players to stop it, though its damage resets to 0% after a point is earned.
Fifteen different Sandbags and eleven different Sandbag Jr.'s appear as background characters in the arena, where they cheer from the bleachers. This makes the arena the only stage not selectable from the stage selection screen in the game to feature background characters.
Although the arena is completely enclosed, it is still possible for a player or the Sandbag to be Star KO'd or Screen KO'd using glitches or Final Smashes via the Final Smash Meter to travel past the ceiling and into the upper blast line.