Other mistake: In the game against Midland Lee there is a shot where the quarterback on Midland Lee is scrambling towards the sideline, if you look closely you can tell the quarterback is wearing a Riddell Revolution helmet. Riddell did not release this helmet till about the year 2000 and it is supposed to be 1988 in the movie.
Continuity mistake: When Boobie Miles receives his diagnosis from the Midland doctor, he gets upset and rips the x-ray film of his injured knee off the wall. In the next shot, he rips it down again.
Continuity mistake: During the playoffs, Carter's helmet is matched up with a helmet that has a "W" logo. But when they are actually playing in the game, they are wearing helmets with a longhorn logo.
Continuity mistake: On the second to last play of the championship game, the coach calls for an injured Don Billingsley to run the football on fourth down because Carter was going to play a prevent defense due to the fact that Permian were supposedly out of running backs due to injuries. But Chris Comer, another running back who was supposedly knocked silly a couple of plays before, was on the field for that play as well.
Factual error: In FNL, there is a scene showing a living room with DVDs in it. DVDs were not even on the market in 1988.
Continuity mistake: In the scene when Boobie Miles walks into the locker room to get his stuff from his locker, his knee brace is on the left leg. In the next shot the brace is on his right leg. In the next shot the brace is on his left leg again as he walks out of the locker room.
Answer: I can only think of two possibilities. It could be that 'taking a knee' is not allowed in this division's rules. Or, getting into the heads of the coaches, their philosophy of the game could be to gain as many points as possible even in a lopsided blowout, honoring the game and continuing sportsmanlike competition to the end.