Measure and cut three 6-foot lengths and two 7-foot lengths of metal or PVC pipe. Metal will make a sturdier frame for your lacrosse goal, but it is more expensive and often must be ordered in pre-cut lengths. PVC is more economical, but it may crack or shatter if it is hit too hard with the ball.
Use either metal solder or PVC adhesive to connect two elbow joints to the ends of the 6-foot-long crossbar pipe, depending on the type of material you have chosen for your lacrosse goal's frame. Using the same type of adhesive, connect one of the 6-foot-long side posts to the open end of each of your two elbow joints. You should now have a U-shaped framework for the front of your goal.
Connect an elbow joint to the bottom of each of the 6-foot-long side posts. Turn the elbow joints so that they are angled backward at 45 degrees toward the center of the goal. When you insert the rear support posts, they should almost be touching at a central point behind the goal's mouth.
Connect one of the 7-foot-long posts to each open end of the elbow joint. Use another elbow joint to connect these two 7-foot-long base support posts where they meet at the back of the goal. You should now have a triangular base for your lacrosse goal.
Use wire or sturdy plastic ties to connect the netting to the framework of your lacrosse goal. The net should be attached to the crossbar, sides, and bottom pipes at the rear of the goal. Trim off any excess so that the netting is pulled tight and does not sag at the back of the goal.