Continuity mistake: When Jon Moxon is sitting on the bench during the Bingville game, reading the novel inside the playbook, the player standing in front of him (wearing a white baseball cap) is named Symonds, and is wearing the number 68. During the halftime of the Gilroy game, right after Moxon rallys the team with his speech in the locker room, Symonds is now wearing the number 9 (he jumps right in front of Moxon). When the players return to the field after the locker room rally to start the second half against Gilroy, during the opening kickoff, Symonds is again wearing the number 68.
Revealing mistake: When Darcy and Lance are "having sex" on the drier and the overweight Billy Bob enters you can see that Paul Walker still has his underwear on (it actually looks a lot like a cup) but this would imply that they are faking the sexual noises.
Continuity mistake: When Billy Bob is drunk and shooting his trophies, one of the trophies he throws changes after it hits the ground.
Continuity mistake: During the game, when Lance gets injured, Mox has to throw the ball to stop the clock. You can hear the announcer say "the clock's still running, the clock's still running" Later in the film where Mox has to stop the clock again, you hear the same announcer say the exact same thing but in a complete sentence, meaning they used a portion of the sentence for earlier in the film.
Continuity mistake: During the last game when Lance is coaching, in one scene he has the headset around his neck, then on his ears and then no headset, and the on his neck and it continues this way for quite a few scenes.
Continuity mistake: When Tweeter drives up to Mox at the convenience store, he says the girls in the car are naked, but if you look closely you can see that the girl in the front seat has a pair of jeans on.
Other mistake: Multiple mistakes are made at the end of the game against the Wildcats. Before the final touchdown, the Wildcats are shown leading 13-0 with 6:00 minutes left in the game. After the touchdown, the Wildcats are shown leading 20-3 with 3 seconds left in the game. Based on Mox's position in the two shots, no other plays happened, meaning that the time and score in one of the shots is incorrect. The clock also continues to run when the touchdown is scored even though it's supposed to stop.
Answer: There's no rule in any sport, at least none that I could find, that requires a team to have, or listen to, a coach. Obviously in most cases it's a good idea, but if the coach were poor and/or working against the interests of the team, the players wouldn't be breaking any rules by simply ignoring them and listening to someone else.