Sybil attack March Madness survivor pool?

A question of the statisticians.

I’ve run a March Madness Survivor Pool for years with hundreds of people and it’s all been manual . This year I want to automate all of this and I want to use a blockchain like Polygon to facilitate the bets and try to make it as decentralized as possible.

My concern is that if it is anonymous, can someone effectively game the system by creating say 1,000 wallets and guaranteeing victory? If so, how many accounts would it take and would be financially reasonable to do so?