Pokemon #1: Well, you're playing in the mile-high stadium, and one of the teams is the Seahawks. It'd only make sense to use a flying Pokemon to get to the top.
Pokemon #2: Mascot Pokemon. You need a cute, little Pokemon to motivate your team to victory! (First evolved form or small Pokemon).
Pokemon #3: Well, what's a football game without the big dude behind you with a beer belly? Also, you need someone to protect your team. Pokemone #3 must be big and bulky.
Pokemon #4: Are you a passing team that needs good weather, or are you a running team that likes it a little chilly. Pokemon #4 must know a move that alters the game field. I.E. Hail, Rain Dance, Sandstorm.
Pokemon #5: Well, you really need speed to win a football game! Pokemon #5 needs to be a Pokemon known for their speed.
Pokemon #6: And, obviously, a game isn't complete without the quarterback. This Pokemon just needs to have arms that look like they can throw a ball. I.E. Sawk, Machoke, Throh.