I really like the idea of the two teams praying together before the game to set the tone. We always pray as a team before and after games, but not usually with the other team. Sometimes, when possible, we'll pray with our opponents after the game. However, what a great way to "set the tone" as you put it!
After all, God gave us the ability to play the game. I believe we should honor Him in the way we play. As our guys coach likes to say, "Whether we win or lose, we will play our hardest for the glory of God!"