The Texas Stadium, home of the NFL Dallas Cowboys, has a hole over the field because the original plans (1971) did not contain enough structural integrity to have a full roof. Given the stadium already cost $35 million, there was not enough money (or time, I presume) to add more structural integrity to fill-in the roof.
Also, will the NFL please stop showing the camera view from behind the kicker when he attempts to kick a field goal. While a cool view, it’s not practical. You can barely see the football, with the backdrop of fans, and the TV viewer can’t tell whether or not the kick goes through the upright.