In each of the cells on a 3×3 board there is a ball of one of four colors. The color of a ball signifies its strength or power. The four colors from the weakest to the strongest are blue, green, red, yellow. The balls can move vertically or horizontally such that when two of them happen in the same cell then, if they are of the same strength both disappear; otherwise, only the weakest of the two disappears. To make a move a player selects a ball and a direction (by clicking on a proper side of the ball. The ball moves in the chosen direction until it reaches the rim of the board or perishes by running into a stronger ball. Balls must interact on each move, i.e., a ball can't move without hitting another ball. The player to make the last move wins.