…the next pick to the people who saw you pick the “winner”. Now half of those people see one team, the other half see you pick the other team, and whoever saw you pick the winner thinks you’ve got a 100% accuracy rate over two games. You could do that for a while and then offer to sell your pick for the Superbowl. Starting with a big enough group in the beginning, this might be really lucrative.
But is it legal?
Here the intent is to commit fraud – deception for the purpose of financial gain. It is deception because you have knowingly misrepresented your ability to predict games, and you have gained financially by selling the pick. So it would be illegal on that basis in most if not all jurisdictions. The actual mechanism by which you create the deception or profit from it are not that important.
Moreover if you accept the money by mail or by digital means and I really wanted to hurt you (and you were in the US), I would go after you for mail fraud or wire fraud, not the scheme itself. These have very harsh penalties in the US and powerful authorities with a vested interest in keeping it that way.
(I am not a lawyer)