The biggest problem I have with the design is the need to lift the corners to insert the final screws. Here is how we go about assembling our field.
Lay out two sides parallel and fasten the panels together top and bottom with the straight brackets.
Attach the corner pieces on the bottom at each end of those two sides with one screw at each bracket.
Assemble the remaining two sides, of 3 panels each, and lay in position. Do not attach any corner pieces.
Raise two adjacent sides into position and attach the top corner bracket. At this point you should have one screw missing on the bottom side of the corner bracket
To avoid lifting and twisting the field sides, we insert the remaining screw for the bottom corner bracket so it is pointing down, serving as a pin (thread the screw into the captive nut and down through the hole in the bracket). See attached photos.
Repeat for the other corners.
Really, the only difference is that one screw in each coner is inserted into the captive nut backwards, top down, so you don’t need to lift the sides and insert it. The screw still pins the bracket in place. We have used this approach for 3 years now, and never ahd a problem with a corner coming apart.