Paint the wood pieces in the colors you picked.Glue them together and let it all dry.
Cut the wood to size. This includes: 2 pieces of 1x1 wood at 2 1/4 inches long2 pieces of 1x1 wood at 3 1/4 inches long4 pieces of 1x1 wood at 2 inches long a1 - 4x4 by 1-inch block Give the pieces a light sand. You can be a little more aggressive on the ends that were cut.
Paint the 4x4 piece green like the grass on the field. Paint all the other pieces yellow. You will need about three coats of paint. Let it dry fully in between each coat.
Once the paint is dry, glue the pieces together. Start with gluing the 2 1/4 pieces perpendicular to the 3 1/4 pieces. This makes the base of the goal posts.
Once dry glue the 2 inch piece to each end of the 3 1/4 piece. Let dry.
If you want now, you can use wood filler and fill in the gaps. Let that dry and sand if needed. Then paint again. I just globbed a little more paint into my gaps.
Use the wood glue and attach the goal posts to each side of the green 4x4 block. Let dry completely.