Assemble the frame by screwing the 2-foot sections of 2x4's to the 36-inch sections of the 2x4's to make a rectangle to support the plywood playing field.
Make legs to hold the board upright by screwing the 13 1/2-inch-long 2x4's to the top of your frame. You can cut the bottom at an angle so it sits flush on the floor if you'd like.
Measure out the foul box 1 1/2 inches above the bottom of the plywood and make it 5 by 8 inches wide. Center this on the plywood.
Go 6 1/2 inches up the center of the board and mark the spot. Cut a 4-inch-diameter base hole above that mark. Go up another 6 1/2 inches to cut the home run circle. Four inches above that is the third base circle, which should be 3 inches from the top of the board.
Mark 5 inches in from the side. Cut out the first base hole that is centered between the bottom three bases and the foul box. Between the home run and the bottom three bases, make the hole for two bases. Center the out hole between the top three bases and the home run hole.
Repeat these same cuts 5 inches in on the other side of the plywood.
Paint or stain the plywood in any fashion you like. Once dry, screw it to the frame, making sure the foul box is closest to the ground and the legs of the frame are at the top of the plywood surface. Label each hole. You're now ready to play beanbag baseball.