The playing field is a right-angled fan-shaped area, and both sides of the right angle are the boundary lines that distinguish the in-bound area from the out-of-bounds area. Within the two sides of the line is the boundary area; Beyond the two sides of this line is out of bounds. Both in-bound and out-of-bounds areas are effective areas for the competition. The boundary is divided into infield and outfield. The infield is square with a base at each corner. The base at the acute angle on the same horizontal plane is home plate, and the counterclockwise direction is first base, second base and third base respectively. The area outside the infield is the outfield. The playing field must be flat without any obstacles.