First Benoni, hosted the provincial Scout and Cub Canoe Polo contests this weekend. They built these nets using thatching laths. Because these nets will be used again, the joints are fastened with screws, but you could just as easily use lashings.
Note the diagonal braces in the front view- one lies at the front of the frame, and one at the back. It is important that these run in opposite directions to make the goalposts rigid.