Those of us who are Christians should walk our talk as well as be respectful of the non-biblical guideline of the Golden Rule. We should do unto others as we would have them do unto us. And breaking the law in order to show off our beliefs or impose those beliefs on others definitely goes against what is right.
We do not need, nor have the right, to announce a Jesus-based prayer across a loud speaker in order to behave in a moral manner on the football field and in the grandstands. In fact it has a Pharisee-type of theatrics to it.
So instead, the loudspeaker announcer could simply remind everyone to respect each other, have fun and enjoy the game - treating it as just what it is: a game.