105
...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?
Well it's not mathematically possible
The formula is p/(2^n)
P would be the number of people you start with, and n is the number of games.
If you start with the population of the US, 350 million people, you can only do this for about 28 matches before you run out of people.
If it makes any difference, American football seasons are only like 16 games.
"only"
I'm pretty sure people would give you money after 10 correct predictions in a row. At that point there are 350k remaining.