The events were supposed to have taken place in 1993. You can see the teams wearing Under Armour gear but UA wasn't made public until 1995-1996 and it was sold to the Georgia Institute of Technology (or Georgia Tech).
The first time we see Junior's last name written on his helmet (inside the locker room), it is written with one capital letter and the rest are small letters. Seconds later, on the practice field, his name is written in all capital letters.
When the Mustangs are going to their first game Jamal Evans is seen wearing a long sleeve shirt and ask Coach for a Mustang shirt and Coach explains to him that they will try to find him a shirt. However, when we see Jamal Evans again he is wearing a Mustang shirt
In the Mustang's first game against the Panthers there is an interception in which the receiving Panther never changes direction and continues to run to the Mustang's end zone. The Panthers are still awarded the touch down as if there were no mistake made.
Dexter and Coach are discussed Willie Weathers' being on the team, saying that they agreed that no killers would be on the team. However, earlier Kelvin Owens had said Junior (who was also on the team) thought he was the king of Samoa because he had killed a Mexican with a baseball bat.
The goof item below may give away important plot points.
When Kelvin Owens is shot, he is shot in the right shoulder and blood is flowing down his right arm. When he appears at the second game vs. the Barrington Panthers, after his shooting, he is wearing a sling on his left arm.