What I have seen is they choose two HS football teams. How I don't know. The teams are made of the QB and two WRs.
Each team gets two throws. The team with the most accumulated yards wins. The slight advantage goes to the "home" team because they know how far they need to throw the ball. If the "visiting" team messes up their two chances the home team doesn't have to gamble. If the visiting team gets a long catch then the home team has to gamble and go for a longer play.
To make it a little more interesting the WRs can't simply start at the line of scrimmage and run 10 yards for a total of 20 yards. If the first receiver catches the ball 10 yards down field the second WR runs the first 10 yards before he gets to his starting point.
They rotate turns. Visiting team, home team, visiting team and home team. I can't remember if the plays are timed or not. The Packers are setting up other halftime items while this is going on. If they are not timed the teams are "encouraged" to complete their plays as quick as possible.
I usually attend the 5th home game with my son, which is tomorrow's game, but I let my son take his new bride in my stead.
Oh, the crowd usually is very supportive of the HS players. While many people are heading to the restrooms and concession stands there is still a pretty lard crowd cheering the guys on and applauding good plays.